Open Cluster M18 (also known as Messier Object 18 or NGC 6613) is an open cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1764 and included in his list of comet-like objects. M18 is situated between the Omega Nebula (M17) and the Sagittarius Star Cloud (M24). Its age is estimated at 32 million years.

M18 is best observed in small telescopes, which show over a dozen of fairly bright stars. It is about 0.2 degrees in diameter, thus appears loose and poor.