Hey, guys. Just a friendly reminder that, in honor of their 20th anniversary, end-of-month bike ride Critical Mass kicks off tonight, and it's going to be a whopper. What is Critical Mass, exactly? As SFist commenter Mike explains, "Critical Mass is Gay Pride for bikes. It's a demonstration of numbers and force. Critical Mass is a temporary seizure of power and space from an otherwise hostile traffic environment."

For those of you new to cycling around the city, and plan on dipping your toes in the pedaling waters tonight, check out our etiquette guide on riding around the city. The festivities commence at Justin Herman Plaza starting at 6pm.

Previously: Critical Mass Breaks Up With SF Bike Coalition