April 8 - U.S. President Barack Obama and Russian President Dmitri Medvedev sign the New START agreement to replace the expired Strategic Arms Reduction Treaty of 1991.
May 3 - The United States announces that it maintains 5,113 nuclear warheads which are actively deployed, in reserve, or in storage.
May 26 - Britain announces that it maintains 225 nuclear warheads, 160 of which are operational.
August 20 - Russia begins installation of uranium-packed fuel rods into Iran's Bushehr reactor.
September - The STUXNET security worm infiltrates Iranian nuclear computers and temporarily halts production of enriched uranium.
November 12 - North Korea reveals to a visiting delegation that it has created a 2,000-centrifuge uranium enrichment facility. North Korea also confirms that it is capable of producing uranium hexaflouride, the necessary element for reprocessing and weaponizing.
December 22 - The United States Senate ratifies the New Strategic Arms Reduction Treaty (New START), which will reduce both US and Russian deployed strategic nuclear weapons to 1,550 each and deployed delivery vehicles to 700 each.
January 19 - The United States and China sign a deal to build a jointly-run nuclear security center in China. This center will be dedicated to preventing proliferation.
February 5 - New START treaty officially takes effect.
March 11 - A 9.0 earthquake and subsequent tsunami strike Japan, causing the Fukushima Daiichi Nuclear Power Plant to shut down. Emergency cooling systems fail, causing the plant to experience partial meltdown. The crisis is labeled at the highest level on the International Nuclear Events Scale
March 19 - Malaysian police discover parts designed for nuclear weapons being smuggled on board a ship to Iran.
May 11 - Russia delivers 30 tons of nuclear fuel to Iran, completing an agreement signed in 1995 between Iran and Russia to build a nuclear power facility.
May 13 - It is revealed that 32 separate nuclear power plants in the United States have failed safety tests after the Fukushima incident.
June 9 - The International Atomic Energy Agency announced that the Fukushima Daiichi plant in Japan has experienced a "melt-through" at three reactors. Significantly more dangerous than a meltdown, a melt-through is considered the worst possible scenario short of an explosion at the nuclear plant.
June 10 - Iran announces to the International Atomic Energy Agency that it will begin enrichment at its new Fordow plant.
July 13 - Funds are put in place to build a shelter over the Chernobyl nuclear reactor that experienced meltdown in 1986.
August 20 - General Electric successfully tests a method of enriching uranium with lasers.
November 23 - Russia announces plans to counter the missile defense system that the US has been planning in Europe.
December 1 - The U.S. State Department releases an updated count of its deployed and reserve strategic nuclear weapons as of September 1, 2011. The U.S. has 822 deployed ICBMs, SLBMs and heavy bombers, while Russia has 516. The number of nuclear warheads deployed on these platforms total 1,790 for the U.S. and 1,566 for Russia.
February 29 - North Korea announces that it will suspend nuclear weapons tests and uranium enrichment activities and allow international inspectors to monitor activities at its Yongbyon nuclear facility.
February 12 - North Korea conducts its third nuclear test. The estimated yield is 8-10 kilotons.
February 12 - North Korea conducts its third known nuclear test. UN condemns the test and places new sanctions on the country.
March 5 - North Korea cuts off all contact with South Korea including the only emergency phone line between the two countries.
March 7 - The United Nations Security Council unanimously passes Resolution against North Korea. Resolution 2094 strengthens existing sanctions by expanding the scope of materials covered and adds additional financial sanctions, including blocking bulk cash transfers. Additional individuals and entities also are identified for asset freezes.
June 19 - US President Barack Obama calls for US-Russia nuclear weapon cuts in a speech in Berlin.
August 10 - India activated the reactor on board the INS Arihant nuclear submarine, the first to be designed and built in India.
September 19 - Iran’s new President Hassan Rouhani makes a pledge that his country would never build nuclear weapons.
November 6 - Sources show that Saudi Arabia has invested in Pakistani nuclear weapons projects, and believes it could obtain atomic bombs at will.
December 18 - Russia deploys tactical ballistic missiles suggesting that Russia is taking a more assertive stance in the region. Since being in power, President Vladimir Putin has made new nuclear delivery systems a top priority.
January 20 - An interim agreement to curb Iran’s nuclear program enters into force. The agreement includes easing sanctions on Iran in return for Iran halting its uranium enrichment.
January 31 - US Defense Department officials acknowledge that officers responsible for safeguarding nuclear weapons had cheated, or were aware of cheating, on monthly tests. As a result 92 Air Force Officers, nearly half of the nuclear launch crew, were suspended.
March 25 - Japan hands over an estimated 1,100 pounds of weapons-grade plutonium to the US.
July 29 - The United States renews its 1958 agreement to share nuclear weapons information with the United Kingdom. Many argue that the Mutual Defense Agreement violates Article I of the Non-Proliferation Treaty.
September 10 - Russia successfully tests a new intercontinental ballistic missile capable of hitting targets up to 5,000 miles away.
November 20 - North Korea threatens fourth nuclear test.
January 13 - The United States rejects North Korean offer to suspend nuclear tests.
January 19 - Russia informs the United States that they will no longer be seeking the United States’ help in securing Russia’s massive weapons-grade uranium stockpile.
January 28 - The United States prepares to develop and build a new generation of Intercontinental Ballistic Missiles (ICBMs) for the Air Force.
March 20 - United States finally admits that Israel has nuclear weapons.
April 15 - United States reveals that it had known about Israel’s nuclear program for over 50 years.
May 22 - The 2015 NPT Review Conference ends in failure after the United States, United Kingdom, and Canada refuse to adopt the final document in defense to Israel’s concerns over language relating to the proposed Middle East Zone free of nuclear weapons. July 14 - World powers reach a deal with Iran on limiting Iranian nuclear activity in return for the lifting of international economic sanctions.
August 19 - China conducts a flight test of its new D-F road mobile intercontinental ballistic missile (ICBM).
North Korea announces that it is improving the quality and quantity of its nuclear arsenal in response to the "reckless hostile policy" of the United States and its allies.
October 19 - After nearly 50 years, the United States announces that it will clean up radioactive contamination caused by a plane crash in 1966 in Palomares, Spain.
January 6 - North Korea conducts its fourth test of a nuclear weapon.
January 12 - Israel receives a fifth Dolphin-class nuclear-capable submarine produced by Germany.
Febuary 7 - North Korea launches a satellite into space, claiming that the launch is for scientific and peaceful purposes.
Febuary 23 - French President Francois Hollande acknowledges that the 193 nuclear tests conducted by France in French Polynesia had serious consequences.
April 11 - Secretary of State John Kerry visits the Hiroshima Peace Memorial Museum, the first sitting U.S. secretary of state to visit the site.
May 12 - The United States’ European missile defense shield goes live, almost a decade after Washington’s initial proposal to protect NATO states from Iran’s alleged increasing nuclear capacity.
May 20 - Pakistan formally applies for entry into the Nuclear Suppliers Group (NSG), after China blocked India’s entry into the 48-member elite group.
May 27 - Barack Obama visits Hiroshima, the first sitting U.S. President to do so.
June 21 - North Korea successfully launches another ballistic missile after a string of failed launches.
August 19 - The U.S.S. Louisiana, a nuclear-armed submarine, collides with the U.S.N.S. Eagleview while conducting routine operations off the coast of Washington State. The ships are damaged, but nobody is injured.
August 24 - North Korea successfully launches a ballistic missile from a submarine. September 5 - North Korea test-fires three missiles toward Japan on the final day of the Group of 20 summit meeting, where the president of South Korea called for an end to North Korea’s provocations.
September 9 - In its fifth test, North Korea claims to have detonated a nuclear warhead. According to South Korea's Meteorological Administration, the blast was estimated to have the explosive power of 10 kilotons. In the wake of the test, American military experts predict that North Korea will have the skills to make a nuclear warhead for a missile by 2020.
September 20 - In the wake of North Korea’s nuclear test, the Chinese government announces an unprecedented criminal investigation into a Chinese conglomerate that potentially provided North Korea with materials that could be used in the production of nuclear weapons.
October 3 - Vladimir Putin signs a decree withdrawing Russia from its plutonium disposal treaty with the U.S., citing deteriorating relations.
December 23 - Intensifying his assertion about increasing American nuclear capabilities, Trump states in an interview, "Let it be an arms race... we will outmatch them at every pass and outlast them all."
January 28 - Iran test-fires a medium-range ballistic missile, in defiance of UN Security Council Resolution 2231.
February 3 - TEPCO said the radiation level in the containment vessel of reactor 2 at the crippled Fukushima No. 1 power plant was 530 sieverts per hour, the highest recorded level since the triple core meltdown in March 2011. TEPCO also announced that there is a 2-meter hole under the pressure vessel in the reactor's primary containment vessel.
July 4 - North Korea tested an ICBM named Hwasong-14. The missile flew for approximately 40 minutes, falling 930 km (580 mi) away from the launch site in the Sea of Japan.
July 28 - North Korea tested another ICBM. The missile's reentry vehicle (RV) was seen by people in Japan as it entered the atmosphere and landed near the northernmost Japanese island, Hokkaido.
July - Abnormal radiation levels are detected across Europe, suspecting an incident in Russia. A study now shows it probably stemmed from a nuclear accident in southern Russia. In November, Russia acknowledged the radiation spike in the Urals, but did not go futher with regards to a possible source. Many think it occurred at Mayak nuclear facility.
September 3 - North Korea conducts another nuclear test. The yield rangews from 70-280 kilotons. North Korea claims it was thermonuclear device.
September 15 - North Korea launched a ballistic missile . It reached a height of 770 km and flew a distance of 3,700 km for 17 minutes over Hokkaido before landing in the Pacific.
September 22 - Iran parades its new medium-range ballistic missile tested in January, the Khoramshahr, with a range of about 2,000 km, in a military parade.
November 28 - North Korea launched an ICBM. It traveled for 50 minutes and reached 2800 miles (4,500 km) in height, both of which were new milestones.
February - The United States completes it Nuclear Posture Review. The review stated the US's intention to not ratify the CTBT and rejects the idea of the Treaty on the Prohibition of Nuclear Weapons.
May 8 - President Trump announces that he is withdrawing the United States from the JCPOA and signs a presidential memorandum to institute the "highest level" of economic sanctions on Iran. In an address following Trump's announcement Iranian President Rouhani announces that Iran will continue negotiations with the other states in the agreement in order to try to continue the deal without the United States.
May 15 - EU High Representative Federica Mogherini meets with the foreign ministers of France, Germany, and the United Kingdom, and the three European countries and Iran in two separate meetings to discuss future coordinated work following the U.S. violation of the JCPOA.
May 24 - The International Atomic Energy Agency (IAEA) reports that Iran is implementing all nuclear-related commitments under the JCPOA in a quarterly report. Iran’s stockpile of uranium enriched to 3.67 percent uranium-235 is 123.9 kg, below the 300 kg limit set by the accord, according to the report.
June 6 - Iran opens a new facility for centrifuge production, an act that does not violate the JCPOA.
June 12 - The United States and North Korea meet in Singapore to discuss nuclear issues. No formal progress was made.
February 1 -The United States annouced that it will withdraw from the Intermediate Nuclear Forces Treaty, claiming that Russia had been violating it.
April 9, - Iranian President Hassan Rouhani announces that Iran will install a cascade of 20 IR-6 centrifuges at Natanz.
May 8, - Iran announces that it will no longer be bound by stockpiles limitations on enriched uranium and heavy water reserves in the JCPOA and could restart construction on its unfinished heavy water reactor at Arak and resume higher-level enrichment in the future if the other parties to the agreement do not deliver on sanctions relief. In late April, Iranian Foreign Minister Javad Zarif told state broadcaster IRIB that Iran was considering leaving the NPT as one of Iran's numerous choices.
July 1, - Iran announces that it breached the 300 kilogram limit on uranium gas enriched to 3.67 percent (202 kilograms of uranium by weight). The IAEA confirms that Iran has exceeded the limit.
July 8, - Iran tells the IAEA it has enriched uranium to "about 4.5 percent" uranium-235 at the Natanz pilot fuel enrichment plant.
August 8 - Five military and civilian specialists were killed was a result of a failed test of an "isotope power source for a liquid-fuelled rocket engine."
August 30 - The IAEA confirms that Iran continues to exceed the 300-kilogram stockpile limit on enriched uranium (correlating to 202.8 kilograms of uranium) and the 3.67 percent enrichment cap established by the JCPOA and reports that Iran has amassed 241.6 kilograms uranium, including 25.1 kilograms uranium enriched to 4.5 percent U-235. September 7 - Iran tells the IAEA that it plans to install and test additional advanced centrifuges with natural uranium at the Natanz pilot fuel enrichment plant. The Agency verifies the installation of 22 IR-4, one IR-5, and 33 IR-6 centrifuges.
September 25 - Iran alerts the IAEA of four additional cascades being configured at the Natanz pilot fuel enrichment plant: one of 20 IR-2m centrifuges, one of 10 IR-5 centrifuges, one of 20 IR-6s centrifuges, and one of 164 IR-6 centrifuges.
October 2 - North Korea test-fired a new-type submarine-launched ballistic missile, named Pukguksong-3, flew about 450 kilometers and reached a maximum altitude of 910 kilometers, making it an intermediate-range ballistic missile.