A bumper sticker is an adhesive label or sticker with a message, intended to be attached to the bumper of an automobile and to be read by the occupants of other vehicles - although they are often stuck onto other objects. Most bumper stickers are about 30 cm by 8 cm (12 in by 3 in) and are often made of PVC.

Bumper stickers can be commercial, religious, secular, humorous, or in support of a sports team or other organization. They may promote or oppose a particular philosophical or political position. In some countries, such as the United States, Bumper stickers are a popular way of showing support for a candidate for a government seat and become more common during election years. In others, such as the United Kingdom, they are rarely seen in any form.

One variety of bumper sticker is the country tag. This is typically used for cars crossing international borders, and is overseen by the United Nations as the Distinguishing Signs of Vehicles in International Traffic, being authorized by the UN's Geneva Convention on Road Traffic (1949) and Vienna Convention on Road Traffic (1968). Often the country code is displayed on the license plate itself.