Plutonium was first produced by Glenn T. Seaborg, Joseph W. Kennedy, Edward M. McMillan and Arthur C. Wohl by bombarding an isotope of uranium, uranium-238, with deuterons that had been accelerated in a device called a cyclotron. This created neptunium-238 and two free neutrons. Neptunium-238 has a half-life of 2.1 days and decays into plutonium-238 through beta decay. Although they conducted their work at the University of California in 1941, their discovery was not revealed to the rest of the scientific community until 1946 because of wartime security concerns.

Plutonium's most stable isotope, plutonium-244, has a half-life of about 82,000,000 years. It decays into uranium-240 through alpha decay. Plutonium-244 will also decay through spontaneous fission.

Only two of plutonium's isotopes, plutonium-238 and plutonium-239, have found uses outside of basic research. Plutonium-238 is used in radioisotope thermoelectric generators to provide electricity for space probes that venture too far from the sun to use solar power, such as the Cassini and Galileo probes. Plutonium-239 will undergo a fission chain reaction if enough of it is concentrated in one place, so it is used at the heart of modern day nuclear weapons and in some nuclear reactors.