The first ride of Critical Mass took place on Friday, September 25, 1992 at 6pm in San Francisco. At that time it was called Commute Clot and it was composed of hundreds of cyclists.

By the time of the fourth ride, the number of cyclists had increased to around100 and the participation continued to grow dramatically, reaching about 1000 riders approximately.
The name "Critical Mass" was soon adopted as a generic label by the riders in similar but independent mass rides, that were initiated in the various locations around the world.
Actually, the group had already existed before 1992 under various names.