Critical Mass is an event held typically on the last Friday of every month in cities around the world, where bicyclists, skateboarders, roller bladers, roller skaters and other self-propelled people take to the streets en masse. Critical Mass has no leaders, and no goals other than to meet once every month and enjoy the security and companionship of riding, rolling and travelling through the city together. The one worldwide slogan, chanted by riders in probably all cities where the ride take place is: "We aren't blocking traffic; we are traffic."