Critical Mass-like bike tours with hundreds of participants took place in Stockholm, Sweden in the early 1970s. But the first ride within the present wave took place on Friday, September 25, 1992 at 6 pm in San Francisco. At that time, the event was known as Commute Clot and was composed of a couple of dozen cyclists who had received flyers on Market Street.
Shortly after this, some participants in that ride went to a local bicycle shop for a screening of Ted White's documentary Return of the Scorcher, about bike culture overseas. In that film, American human powered vehicle and pedicabs designer George Bliss noted that, in China, both motorists and bicyclists had an understood method of negotiating intersections without signals. Traffic would "bunch up" at these intersections until the backlog reached a "critical mass", at which point that mass would move through the intersection. That term from the movie was applied to the ride, and the name caught on, replacing "Commute Clot" by the time of the second event.
By the time of the fourth ride, the number of cyclists had increased to around 100 and participation continued to grow dramatically, reaching about 1,000 riders, on average.
The name was soon adopted as a generic label by participants in similar but independent mass rides that were either initiated in various locations around the world at around the same time, or had already existed before 1992 under other names. It is estimated that there are Critical Mass-type rides in more than 325 cities to date. The term "masser" is sometimes applied to a frequent participant.
