Critical Mass is an event held in cities around the world, where cyclists, skateboarders, roller bladers, roller skaters and other self-propelled people take to the streets en masse. Critical Mass is not led, and as a group has 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 general philosophy is expressed by a widely used slogan: "We aren't blocking traffic; we are traffic."