Sputnik 1 (; see § Etymology) was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program. It sent a radio signal back to Earth for three weeks before its three silver-zinc batteries ran out, and continued in orbit for two months until atmospheric drag caused it to fall back into the atmosphere on the 4th of January 1958.

It was a polished metal sphere 58 cm (23 in) in diameter with four external radio antennas to broadcast radio pulses. Its radio signal was easily detectable by amateur radio operators, and the 65 orbital inclination made its flight path cover virtually the entire inhabited Earth.

The satellite's unanticipated success precipitated the American Sputnik crisis and triggered the Space Race, part of the Cold War. The launch was the beginning of a new era of political, military, technological and scientific developments. The word sputnik is Russian for satellite when interpreted in an astronomical context; its other meanings are spouse or traveling companion.Tracking and studying Sputnik 1 from Earth provided scientists with valuable information. The density of the upper atmosphere could be deduced from its drag on the orbit, and the propagation of its radio signals gave data about the ionosphere.

Sputnik 1 was launched during the International Geophysical Year from Site No.1/5, at the 5th Tyuratam range, in Kazakh SSR (now known as the Baikonur Cosmodrome). The satellite travelled at a peak speed of about 8 km/s (18,000 mph), taking 96.20 minutes to complete each orbit. It transmitted on 20.005 and 40.002 MHz, which were monitored by radio operators throughout the world. The signals continued for 21 days until the transmitter batteries ran out on 26 October 1957. Sputnik 1 burned up on 4 January 1958 while reentering Earth's atmosphere, after three months, 1,440 completed orbits of the Earth, and a distance traveled of about 70,000,000 km (43,000,000 mi).

The Space Race was a 20th-century competition between two Cold War adversaries, the Soviet Union and the United States, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between the two nations following World War II. The technological advantage demonstrated by spaceflight achievement was seen as necessary for national security, and became part of the symbolism and ideology of the time. The Space Race brought pioneering launches of artificial satellites, robotic space probes to the Moon, Venus, and Mars, and human spaceflight in low Earth orbit and ultimately to the Moon.The competition began in earnest on August 2, 1955, when the Soviet Union responded to the American announcement four days earlier of intent to launch artificial satellites for the International Geophysical Year, by declaring they would also launch a satellite "in the near future". The developments in ballistic missile capabilities made it possible to take the competition between the two states into space. This competition gained public attention with the "Sputnik shock", when the USSR achieved the first successful artificial satellite launch on October 4, 1957 of Sputnik 1, and subsequently when the USSR sent the first human to space with the orbital flight of Yuri Gagarin on April 12, 1961. The USSR demonstrated an early lead in the race with these and other firsts over the next few years, reaching the Moon for the first time with the Luna programme by employing robotic missions.

After US president John F. Kennedy raised the stakes by setting a goal of "landing a man on the Moon and returning him safely to the Earth", both countries worked on developing super heavy-lift launch vehicles, with the US successfully deploying the Saturn V, which was large enough to send a three-person orbiter and two-person lander to the Moon. Kennedy's Moon landing goal was achieved in July 1969, with the flight of Apollo 11, a singular achievement considered by the Americans as overshadowing any combination of Soviet achievements that have been made. However, such an opinion is generally contentious, with others attributing the first man in space as being a much larger achievement. The USSR pursued two crewed lunar programs, but did not succeed with their N1 rocket to launch and land on the Moon before the US, and eventually canceled it to concentrate on Salyut, the first space station programme, and the first time landings on Venus and on Mars. Meanwhile, the US landed five more Apollo crews on the Moon and continued exploration of other extraterrestrial bodies robotically.

A period of détente followed with the April 1972 agreement on a co-operative Apollo–Soyuz Test Project (ASTP), resulting in the July 1975 rendezvous in Earth orbit of a US astronaut crew with a Soviet cosmonaut crew and joint development of an international docking standard APAS-75. Being considered as the final act of the Space Race, the competition would only gradually be replaced with cooperation. The collapse of the Soviet Union eventually allowed the US and the newly founded Russian Federation to end their Cold War competition also in space, by agreeing in 1993 on the Shuttle–Mir and International Space Station programs.