Kosmos 18 (Russian: Космос 18 meaning Cosmos 18) or Zenit-2 No.11 was a Soviet optical film-return reconnaissance satellite launched in 1963. A Zenit-2 satellite, Kosmos 18 was the eleventh of eighty-one such spacecraft to be launched and had a mass of 4,730.0 kilograms (10,427.9 lb).
Kosmos 18 was operated in a low Earth orbit. On 30 May 1963 it had a perigee of 203 kilometres (126 mi), an apogee of 278 kilometres (173 mi), with inclination of 64.9 degrees and an orbital period of 89.31 minutes. Having spent nine days in orbit, the spacecraft was deorbited on 2 June 1963. Its return capsule descended under parachute and was recovered by Soviet forces. In addition to its imaging mission, Kosmos 18 was used to conduct measurements of radiation levels in low Earth orbit.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.