The Sputnik program was a series of unmanned space missions launched by the Soviet Union in the late 1950s to demonstrate the viability of artificial satellites. The name "Sputnik" ("Спутник") comes from Russian where it means "satellite" or "fellow traveller".
Sputnik 1 was launched on October 4, 1957. See that page for mission details.
Sputnik 2 was launched some months later, and carried the first living passenger, a dog named Laika. The mission planners did not provide for the safe return of the spacecraft or its passenger, making Laika the first space casualty.
The first attempt to launch Sputnik 3 on February 3, 1958 failed, but the second on May 15 succeeded, and it carried a large array of instruments for geophysical research. Its tape recorder failed, however, making it unable to measure the Van Allen radiation belts.
Sputnik 4 was launched into orbit two years later on May 15, 1960.
Sputnik 5 was launched into orbit on August 19, 1960 with the dogs Belka and Strelka (Russian for "Squirrel", or more likely "Whitey" from Russian "belyj", which means "white", and "Little Arrow"), 40 mice, 2 rats and a variety of plants on-board. The spacecraft returned to earth the next day and all animals were recovered safely.
All Sputniks were carried to orbit by the R.7 launch vehicle, originally designed to carry ballistic warheads.
The surprise launch of Sputnik 1, coupled with the spectacular failure of the first two Project Vanguard launch attempts, shocked the United States, which responded with a number of early satellite launches including Explorer I, Project SCORE, Advanced Research Projects Agency and Courier 1B. Sputnik also led to the creation of NASA and major increases in U.S. Government spending on scientific research and education. See: Sputnik crisis.