Critical Mass is a monthly bicycle ride to celebrate cycling and to assert cyclists' right to the road. The idea started in San Francisco in September 1992 and quickly spread to cities all over the world. This site attempts to be the most complete guide to local Critical Mass rides around the globe. Critical Mass has a different flavor from city to city -- there's a big variety in size, respect of traffic laws (or lack thereof), interaction with motorists, and intervention by police. So if you want to know more about Critical Mass, you'll really need to find out what your local ride is like. For those who must know more right now, here's a link to Phoenix, Arizona CM, which I suppose is a "typical" CM ride, if there is such a thing. Critical Mass has no leaders, and no central organization licenses rides. In every city that has a CM ride, some locals simply picked a date, time, and location for the ride and publicized it, and thus the ride was born. CM is an idea and an event, not an organization. You can't write to "Critical Mass" -- certainly not by writing to me. Some CM riders try to tie up traffic as much as possible and be otherwise confrontational with motorists. Such riders are missing the point about Critical Mass. CM is a celebration of cycling, not a war against motorists. CM is about asserting our right to the road, not denying others their right to the road. Those who want to play juvenile games are encouraged to stay at home instead.