1962: North Korea sets up an atomic energy research center with Soviet help.
1964: China helps North Korea prospect for uranium.
1967: North Korea starts up a small Soviet-supplied reactor.
1974: North Korea joins the International Atomic Energy Agency (IAEA).
1975: North Korea produces a few grams of plutonium.
1977: North Korea agrees to international inspection of Soviet-supplied equipment.
1977: Kang Song-San, a high party official, visits China's Lop Nur nuclear test site.
1979: North Korea starts to build a 5 MWe (30 MWt) reactor at Yongbyon that can produce approximately enough plutonium for one bomb a year.
1985: North Korea signs the Nuclear Nonproliferation Treaty (NPT), promising not to produce nuclear weapons and to open all nuclear sites to inspection. In return, the Soviet Union promises to supply North Korea with several large power reactors.
1985: North Korea starts to build a 50-MWe (200-MWt) reactor that can produce enough plutonium for seven to ten bombs a year. It also starts to build a large plant to process plutonium into weapon-ready form.
1986: The 5 MWe (30 MWt) reactor at Yongbyon begins to produce plutonium.
July 1987: North Korea misses the first 18-month deadline for the beginning of international inspections. Inspectors grant an 18-month extension.
December 1988: North Korea misses a second deadline for beginning international inspections, and demands "legal assurances" that the U.S. won't threaten it with nuclear weapons.
1989: According to the Central Intelligence Agency (CIA), North Korea secretly unloads enough plutonium-bearing fuel from its 5 MWe (30 MWt) reactor to make one or two nuclear bombs.
1989: North Korea begins to process plutonium into nuclear-ready form.
September 1989: North Korea starts to build a 200-MWe (800-MWt) reactor that can produce enough plutonium for 30 to 40 bombs a year.
February 1990: North Korea threatens to drop out of the NPT unless the U.S. removes all nuclear weapons from the Korean peninsula.
March 1990: U.S. fines German firm Degussa for illegally supplying U.S.-origin reactor material to North Korea.
November 1990: North Korea tries to buy electronic components for bomb triggers from a U.S. company.
December 1990: South Korean press reports 70 to 80 high-explosive tests of bomb components in North Korea.
1990: North Korea tests its large plutonium processing plant, showing it is operational.
1990: North Korea starts up its new plant to process uranium for reactor fuel.
1990: A KGB report asserts that North Korea has developed a nuclear device, but has decided not to test the device in order to avoid international detection.
October 1991: U.S. begins to remove nuclear weapons from South Korea.
December 1991: North and South Korea agree to denuclearize the peninsula and not to produce, test, receive, deploy or possess nuclear weapon fuel or weapons, or the means to make them.
January 1992: North Korea agrees to regular IAEA inspections of its nuclear facilities.
1992: The IAEA finds evidence that North Korea had processed more than the 80 grams of plutonium it had disclosed to the Agency.
1992: According to U.S. intelligence, North Korea buries the first floor of a two-story building believed to contain waste from plutonium extraction.
1993: U.S. aerial photographs and IAEA chemical analysis data confirm the existence of a nuclear waste dump and inconsistencies in North Korea's declaration of nuclear materials.
February 1993: IAEA inspectors ask to see two undeclared sites, on suspicion that secret plutonium processing will be revealed, and allow one month for compliance.
March 1993: North Korea rejects the request and announces its intention to withdraw from the NPT.
April 1993: The IAEA declares North Korea in non-compliance, and refers the matter to the U.N. Security Council.
June 1993: North Korea "suspends" its withdrawal from the NPT but continues to bar inspectors from full inspection.
August 1993: IAEA inspectors are restricted to working at night by flashlight.
October 1993: North Korea repudiates the NPT and breaks off talks with inspectors.
November 1993: North Korea breaks off denuclearization talks with South Korea.
November 1993: A North Korean diplomat is expelled from Russia for trying to hire Russian scientists.
December 1993: North Korea offers to let inspectors into only five of seven declared nuclear sites, barring them from the 5MWe (30-MWt) reactor, the plutonium processing plant and two undeclared sites. Inspectors say their cameras no longer work.
December 1993: U.S. intelligence says North Korea has a "better than even" chance of possessing one or two bombs.
December 1993: The IAEA indicates it can no longer provide any meaningful assurance on the peaceful use of North Korea's declared nuclear installations.
1993: North Korea manufactures fuel for its 50-MWe (200-MWt) reactor.
January 1994: North Korea agrees to a one-time inspection of all seven declared sites, but balks at procedures.
February 1994: North Korea agrees to inspection procedures but delays inspectors' visas and continues to bar inspectors from undeclared sites.
March 1994: Inspectors find seals broken, are denied access to crucial equipment and cannot certify North Korean compliance.
March 1994: IAEA inspectors find evidence that North Korea is constructing a second plutonium processing line, which would double plutonium production.
May 1994: North Korea shuts down its 5 MWe (30 MWt) reactor and removes about 8,000 fuel rods, which could be reprocessed into enough plutonium for 4-5 nuclear weapons. The IAEA is denied permission to inspect the removed fuel rods.
June 1994: The IAEA adopts a resolution concluding that North Korea is "continuing to widen its non-compliance… by taking actions which prevent the Agency from verifying the history of the reactor core and from ascertaining whether nuclear material from the reactor had been diverted." Additionally, the IAEA suspends all non-medical technical assistance to North Korea.
June 1994: North Korea withdraws its membership from the IAEA.
October 1994: U.S. and North Korea conclude an "Agreed Framework," under which North Korea will freeze and eventually dismantle its graphite-moderated reactors and related facilities, and will safely store spent fuel from the 5MWe (30 MWt) reactor. In exchange, the U.S. agrees to organize a consortium that will provide North Korea with light-water reactors and will make arrangements to provide heavy heating oil during construction of the light-water facilities.
1994: IAEA inspectors confirm North Korea has frozen its nuclear program and stopped construction on the unfinished reactors.
1995: U.S., Japan and South Korea establish the KEDO consortium, which will provide North Korea with two South Korean-manufactured light-water reactors, worth $4.6 billion, financed primarily by South Korea and Japan.
September - December 1996: A North Korean submarine, believed to be spying, runs aground off the coast of South Korea. South Korea kills seven suspected crewmen. In response to the submarine incident, South Korea delays progress on the Agreed Framework. China joins the U.N. Security Council in criticizing North Korea and expressing "serious concern" about the incident. North Korea apologizes to South Korea for the September submarine incident, and promises to prevent the recurrence of similar incidents in the future.
August 1997: Construction begins on two light-water nuclear reactors being built in North Korea as part of the 1994 Agreed Framework with the United States.
July 1998: The U.S. General Accounting Office (GAO) reports that North Korea is refusing to allow IAEA inspectors full access to its nuclear sites.
March 1999: A U.S. Department of Energy intelligence report allegedly claims that North Korea is working on uranium enrichment techniques.
May 1999: A team of American nuclear specialists arrives in North Korea to begin an inspection of what is suspected of being an underground nuclear weapons site at Kumchangri. No evidence of nuclear activity is found.
July 1999: A U.S. intelligence report claims that North Korea has between 25 and 30 kilograms of weapon-grade plutonium, enough to make several nuclear warheads.
May 2000: A second team of U.S. inspectors visits the Kumchangri underground facility, and again finds no evidence of nuclear activity.
October 2000: The CIA assesses that North Korea has processed enough plutonium for at least one, and possibly two, nuclear weapons.
May 2001: North Korea threatens to pull out of the 1994 Agreed Framework, saying the United States has failed to live up to its obligations under the agreement.
June 2001: The IAEA says it is unable to verify that North Korea is not diverting nuclear material for military purposes, as North Korea has not provided inspectors with sufficient access.
September 2001: KEDO begins excavation work for the first light-water reactor.
March 2002: President Bush decides not to certify North Korea's compliance with the 1994 Agreed Framework before sending fuel oil to Pyongyang, indicating the United States does not have enough information to determine whether North Korea is complying with the agreement. He decides, however, to grant a waiver, allowing the fuel oil shipments to continue.
October 2002: The United States claims that North Korea acknowledged to a U.S. delegation headed by Assistant Secretary of State James A. Kelly that North Korea has been secretly enriching uranium. The admission was prompted by U.S. intelligence indicating North Korea was trying to acquire large amounts of high-strength aluminum, which can be used in equipment to enrich uranium.
October 2002: U.S. intelligence reportedly concludes that Pakistan was a major supplier of critical equipment to North Korea's newly-revealed enrichment program.
November 2002: KEDO decides to suspend heavy fuel oil shipments to North Korea until North Korea takes steps to dismantle its nuclear program.
December 2002: North Korea reportedly succeeds in purchasing from a Chinese company 20 tons of tributyl phosphate (TBP), which can be used to extract plutonium from spent reactor fuel.
December 2002: The IAEA announces North Korea moved 1,000 fresh nuclear fuel rods to a storage facility at the Yongbyon reactor site.
December 2002: North Korea decides to lift the freeze on its nuclear facilities and orders IAEA inspectors to leave the country.
January 2003: North Korea announces it is pulling out of the NPT and rebuffs demands that it allow a return of U.N. inspectors.
January 2003: U.S. spy satellites detect trucks in North Korea that appear to be moving the 8,000 spent fuel rods from storage.
February 2003: North Korea announces it has restarted its nuclear facilities.
February 2003: The IAEA declares North Korea in non-compliance with its inspection obligations and sends the issue to the U.N. Security Council.
February 2003: U.S. spy satellites show a steady stream of activity around North Korea's plutonium reprocessing plant. The activity indicates preparation to activate the facility.
April 2003: French and German authorities reportedly seize 214 ultra-strong aluminum pipes aboard a French cargo ship destined for North Korea, where they would reportedly be used in gas centrifuges for uranium enrichment. The shipment was part of a larger order by North Korea to acquire up to 2,000 such pipes, enough for 3,500 centrifuges.
April 2003: During discussions in Beijing among the United States, North Korea and China, a North Korean official says North Korea has nuclear weapons.
April 2003: According to the CIA, North Korea threatens to "transfer" or "demonstrate" its nuclear weapons during the six party talks in Beijing, according to an unclassified CIA report to Congress. It repeats this threat later in the year.
May 2003: A South Korean official says the United States has a satellite photo showing smoke coming from radiation and chemical labs at Yongbyon (signaling the site may be reprocessing spent fuel rods).
May 2003: North Korea nullifies a 1992 agreement with South Korea to keep the peninsula free of nuclear weapons.
June 2003: North Korea announces its intentions of building nuclear weapons in an attempt to decrease the size of its conventional military forces.
June 2003: The CIA reportedly believes that North Korea is developing technology to make nuclear warheads small enough to fit on missiles.
July 2003: The United States reportedly believes North Korea has begun to process spent fuel rods.
July 2003: South Korean news indicates North Korea claimed to have restarted the 5 MWe (30 MWt) reactor at Yongbyon, as well as to have resumed construction on two other reactors frozen under the 1994 Agreed Framework.
July 2003: North Korean officials say they have finished producing enough plutonium from the 8,000 spent fuel rods for six bombs, which they intend to weaponize quickly.
July 2003: South Korean intelligence confirms North Korea has performed 70 high explosives tests.
August 2003: Six party talks between North Korea and the United States, South Korea, China, Japan, and Russia are held in Beijing. North Korea says it would eliminate its nuclear weapons program if the U.S. first signed a "non-aggression treaty."
September 2003: Chinese authorities at the China-North Korea border stop a shipment of chemicals that could have been used in North Korea's nuclear program, according to an unclassified CIA report.
October 2003: North Korea confirms that in June 2003 it completed reprocessing all of the 8,000 spent fuel rods previously under IAEA safeguards, and announces that all of the plutonium thus derived was being used to increase the size of North Korea's nuclear deterrent force.
October 2003: New intelligence reportedly estimates that North Korea may have produced at least one new nuclear weapon in recent months.
October 2003: Hans-Werner Truppel, a German national, is charged with exporting aluminum tubing for North Korea's uranium enrichment program.
November 2003: The CIA tells Congress that it believes that North Korea is able to turn nuclear fuel into functioning weapons without performing a full nuclear test.
November 2003: The United States and its allies announce that beginning December 1, they will suspend all work for one year on a nuclear power project in North Korea that was part of the 1994 Agreed Framework.
January 2004: A U.S. delegation spends a day at the Yongbyon nuclear complex, where it is shown what North Korea claims is weapons-grade plutonium. A member of the delegation indicates the cooling pond there is empty and that the 5 MW(e) reactor "appears to be operating smoothly."
February 2004: The second round of the six party talks is held in Beijing.
March 2004: A CIA classified intelligence report reportedly concludes that North Korea probably received a comprehensive nuclear package from Pakistan's Khan Research Laboratories, similar to that received by Libya, which included all the equipment and technology needed to produce uranium-based nuclear weapons.
April 2004: Pakistani nuclear scientist Abdul Qadeer Khan is reported to have told investigators that during a 1999 trip to North Korea, he was shown three nuclear devices. It is unclear whether he would have had the expertise to distinguish between an actual weapon and a mock-up.
April 2004: U.S. intelligence prepares to revise its estimate of the number of nuclear weapons possessed by North Korea from "possibly two" to at least eight.
June 2004: The third round of six party talks is held in Beijing. North Korea includes a ban on nuclear transfers in a nuclear freeze proposal it puts forward according to an unclassified CIA report.
February 2005: North Korea announces that it has "manufactured" nuclear weapons and indefinitely suspends its participation in the six party talks.
April 2005: North Korea reportedly shuts down the 5 MW(e) (30 MWt) reactor at Yongbyon.
July-September 2005: The fourth round of six party talks is held in Beijing, where the parties agree to a Joint Statement of Principles. They reaffirm their commitment to peacefully denuclearizing the Korean peninsula. North Korea agrees to abandon its nuclear weapons and nuclear programs and to return to the NPT and to IAEA safeguards at an early date in exchange for economic cooperation and energy assistance.
November 2005: The fifth round of six party talks is held. Discussions end inconclusively due to North Korean displeasure with the U.S. freezing North Korea's accounts in Macau's Banco Delta Asia (BDA) in September.
October 2006: North Korea conducts its first nuclear weapons test. U.S. intelligence confirms that an underground nuclear explosion of less than one kiloton occurred on October 9 near P'unggye, North Korea.
October 2006: The U.N. Security Council adopts resolution 1718 condemning North Korea's nuclear test and imposing a range of sanctions. Sanctions prohibit the import to or export from North Korea of battle tanks, heavy artillery, combat aircraft, and items which could contribute to its nuclear, ballistic-missile, or other weapons of mass destruction programs.
October 2006: After analyzing atmospheric sampling data, U.S. intelligence agencies reportedly conclude that the nuclear explosive device tested by North Korea on October 9 was plutonium-based.
February - March 2007: Two rounds of six party talks are held.
July-August 2007: North Korea shuts down the Yongbyon complex and an uncompleted reactor at Taechon. IAEA inspectors are allowed back into the country to put Yongbyon under safeguards. In exchange, South Korea delivers 50,000 metric tons of heavy fuel oil.
September 2007: An Israeli airstrike destroys Syria's unfinished Al Kibar nuclear reactor in Dair Alzour. The reactor was being built with North Korean assistance.
September - October 2007: Another round of six-party talks is held. North Korea agrees to a set of "disablement actions" at the three main facilities at Yongbyon - the 5 MW(e) experimental reactor, the Radiochemical Laboratory, and the Fresh Fuel Fabrication Plant - and to provide a complete list of all its nuclear programs.
November 2007: North Korea begins to dismantle the main facilities at Yongbyon, with U.S. experts present.
February 2008: A U.S. delegation of nuclear experts visits the Yongbyon complex and verifies that North Korea has completed 10 of the 12 "disablement actions" at the facility.
April 2008: At a bilateral meeting in Singapore, the United States and North Korea reportedly reach a tentative agreement whereby Pyongyang will finish disabling facilities at Yongbyon and provide a full accounting of its plutonium stockpile. The agreement does not address Pyongyang's uranium enrichment work or its past involvement at Syria's Al Kibar nuclear reactor.
June 2008: Another round of six party talks is held. North Korea submits a declaration of its nuclear programs to the Chinese government.
June 2008: U.S. President George Bush signs Executive Order 13466, targeting North Korean vessels and continuing restrictions on North Korean property.
July 2008: North Korea demolishes the cooling tower at Yongbyon.
August 2008: India reportedly blocks an Ilyushin-62 jet owned by North Korea's Air Koryo from delivering cargo to Iran, in response to U.S. concerns that it could be carrying nuclear materials, long-range missile components, or other potentially lethal cargo.
September 2008: North Korea reportedly bars IAEA inspectors from the Yongbyon complex, announcing that it will reactivate the facility.
October 2008: The United States removes North Korea from its list of state sponsors of terrorism after Pyongyang allows international inspectors back into Yongbyon and resumes dismantling its plutonium processing plant.
April 2009: North Korea ceases cooperation with the IAEA and announces its withdrawal from the six-party talks. Agency inspectors remove all IAEA seals and turn off surveillance cameras at Yongbyon before leaving the country.
May 2009: North Korea conducts its second nuclear weapons test. The estimated yield is between two and seven kilotons.
June 2009: The U.N. Security Council adopts resolution 1874 condemning North Korea's nuclear test and imposing additional sanctions. The resolution empowers all member states to inspect suspicious cargo and to seize prohibited items from North Korean vessels and aircraft.
November 2009: North Korea announces that it has restarted its reprocessing facilities at Yongbyon and has reprocessed 8,000 spent fuel rods.
February 2010: Anonymous diplomatic and military sources reportedly announce that North Korea supplied Syria with approximately 45 tons of uranium diuranate (yellowcake) in 2007.
August 2010: U.S. President Barack Obama signs Executive Order 13551, targeting North Korea's weapons proliferation network.
November 2010: North Korea reveals to a visiting U.S. delegation of experts that it has constructed a uranium enrichment facility equipped with 2,000 centrifuges and is in the early stages of building an experimental light water reactor with a capacity of 100 MW(th) (app. 25-30 MW(e)) at the Yongbyon complex.
August 2012: The IAEA reports that North Korea has made "significant progress" over the past year in the construction of a 100 MW(th) light water reactor at Yongbyon.
August 2012: Japan seizes five controlled aluminum alloy rods from the Wan Hai 313, a container ship originating in North Korea destined for Myanmar via Dalian, China.
December 2012: U.S. and South Korean intelligence officials reportedly detect what are believed to be additional uranium enrichment facilities in North Korea using satellite imagery.
January 2013: The U.N. Security Council adopts resolution 2087 imposing additional sanctions against entities and individuals involved in North Korea's nuclear and ballistic missile programs.
February 2013: North Korea conducts its third nuclear weapons test. While yield estimates vary, it is believed to be approximately 6-9 kilotons.
March 2013: The U.N. Security Council adopts resolution 2094 condemning North Korea's nuclear test and imposing additional sanctions.
March 2013: North Korea begins the expansion of a facility reported to house its uranium enrichment workshop at the fuel fabrication plant at Yongbyon.
April 2013: North Korea's General Bureau of Atomic Energy announces that it will restart all the nuclear facilities at Yongbyon, including the enrichment plant and the 5 MW(e) reactor.
May 2013: Bank of China reportedly announces that it will close the accounts of, and stop all transactions with, North Korea's Foreign Trade Bank, which facilitates transactions for North Korea's arms smuggling networks and unconventional weapons programs.
August 2013: The IAEA detects steam discharges and the outflow of cooling water from the 5 MW(e) reactor at Yongbyon using satellite imagery.
September 2013: China reportedly publishes a list of dual-use nuclear products and technologies banned from export to North Korea. Banned items included nickel powder, radium, flash X-ray generators, and microwave antennas.
January 2014: The U.S. Director of National Intelligence assesses that North Korea has restarted the reactor at Yongbyon and expanded its enrichment facilities at the complex.
November 2014: Satellite imagery reportedly detects activity at the reprocessing facility at Yongbyon that is consistent with preparations for commencing operations.
February 2015: Chinese nuclear experts assess that North Korea may have assembled 20 nuclear warheads, with the capacity to produce enough weapons grade uranium for an additional eight to ten warheads per year, considerably higher than previous estimates.
May 2015: U.S. intelligence sources tell Reuters that between 2009 and 2010 Washington made an unsuccessful attempt to attack North Korea's nuclear weapons program with a version of the Stuxnet computer virus.
October - December 2015: North Korea shuts down the 5MW(e) reactor at Yongbyon to remove spent fuel, according to the IAEA.
December 2015: North Korean leader Kim Jong Un claims that his country has developed a hydrogen bomb.
January 2016: North Korea conducts its fourth nuclear weapons test, claiming it was of a hydrogen bomb. The United States reportedly assesses that the test may have involved components of such a bomb, but not a fully functioning device. Initial estimates of the yield range from 6-10 kilotons.
January - July 2016: North Korea reprocesses spent fuel at the Radiochemical Laboratory at Yongbyon, according to the IAEA.
March 2016: The U.N. Security Council adopts resolution 2270, condemning North Korea's nuclear test and imposing additional sanctions. The resolution requires the inspection of all cargo vessels going to or coming from North Korea, and generally prohibits making vessels and aircraft available to North Korea.
March 2016: North Korea claims that it has successfully developed miniaturized nuclear warheads to fit on ballistic missiles.
August 2016: North Korea's Atomic Energy Institute tells Japan's Kyodo News Agency that it has reprocessed spent nuclear fuel "from a graphite-moderated reactor," and that it has been producing highly-enriched uranium.
September 2016: North Korea conducts its fifth nuclear weapons test, claiming that it has standardized nuclear warhead production. Initial estimates of the yield range from 10-20 kilotons.
September 2016: A report issued by U.S. and South Korean researchers indicates that Liaoning Hongxiang Group, a Chinese conglomerate, has supplied North Korea with goods with military and nuclear applications as recently as 2015.