Critical Mass is an event typically held on the last Friday of every month in cities around the world where bicyclists take to the streets en masse. Critical Mass events have no official leader. Participants meet at a set location and time and travel as a group through city streets. Critical Mass rides are self-organized, non-commercial and non-competitive, and they operate with diffused and informal decision-making. Participants have differing purposes for the event, such as demonstrating the advantages of cycling in a city, bringing attention to issues of facilities and safety, enjoying car-free social time on city streets, confronting police, motorists and other symbols of the status quo, and a variety of other purposes, many unstated.