Six flags were planted on the Moon by Apollo astronauts, but not all of them may still be standing, as of 2014. Apollo 11's flag was most likely knocked over by the rocket blast of the returning lunar module.
The Apollo program lasted between 1961 and 1975 and resulted in six successful manned missions to the Moon. Flags were planted by the Apollo astronauts at the site of each landing and, decades later, all but the Apollo 11 flag are still standing, as of 2014. The flags are thought to have been bleached of all color from constant unprotected exposure to the Sun's ultraviolet rays.