Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission began in February 2007 as a constellation of five NASA satellites (THEMIS-A through THEMIS-E) to study energy releases from Earth's magnetosphere known as substorms, magnetic phenomena that intensify auroras near Earth's poles. The name of the mission is an acronym alluding to the Titan Themis.

Three of the satellites orbit the Earth within the magnetosphere, while two have been moved into orbit around the Moon. Those two were renamed ARTEMIS for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun. THEMIS-B became ARTEMIS-P1 and THEMIS-C became ARTEMIS-P2. ARTEMIS-P1 and -P2 together comprise the THEMIS-ARTEMIS mission.

The THEMIS satellites were launched 17 February 2007 from SLC-17B aboard a Delta II launch vehicle. Each satellite carries five identical instruments, including a fluxgate magnetometer (FGM), an electrostatic analyzer (ESA), a solid state telescope (SST), a search-coil magnetometer (SCM) and an electric field instrument (EFI). Each probe has a mass of 126 kg (278 lb), including 49 kg (108 lb) of hydrazine fuel.

THEMIS data can be accessed using the SPEDAS software. Canada, Austria, Germany, and France also contributed to the mission.