Bike to Work Day is a day which is designated for the promotion of bicycle commuting. In the United States, where May is National Bike Month, Bike to Work Day is often scheduled to fall during the month of May, when weather will be favorable for bicycle commuting. However, potentially any day of the year could be designated as Bike to Work Day, and one is by no means limited to one Bike to Work Day each year.

Typically, a city council or another form of local government declares a particular day to be Bike to Work Day, and then the day is promoted. Often, members of city government will choose to cycle to work themselves on Bike to Work Day, sometimes leading rides into the downtown area and encouraging journalists to join them. It is common to see photographs in the newspaper of civic leaders locking their bikes to bike racks, riding down the street in a bike lane, or socializing with other cyclists on Bike to Work Day, to encourage all citizens to do the same.

There are a number of advantages to bicycle commuting, all of which are promoted heavily on National Bike Month and Bike to Work Day. Cyclists get exercise on their way into work, avoid using costly fuel, and often avoid the worst of the traffic, as cyclists can slip around the obnoxious traffic jams which plague many cities. Especially for cities with a population interested in the environment, Bike to Work Day is used to promote other environmentally sound practices, encouraging people to make small changes in their daily lives for the benefit of the world as a whole.

It is not uncommon to see various promotions bundled in with Bike to Work Day. For example, local service organizations might hand out bike helmets, safety lights, and other tools to make biking safer and more enjoyable. Bike to Work Day may also be used as an occasion to unveil new bike lanes, bike racks, and other city installations which promote cycling, ranging from designated bike paths to showering facilities at the workplace which allow bikers to sluice off after their ride in.

The goal of Bike to Work Day is to get more people biking rather than driving, by demonstrating that it is easy, fun, and safe to bike to work. This is one reason why the month of May is typically chosen for the event, because the weather in May tends to be mild and favorable, ideal for cycling.