In many sports, a competition number is used to identify competitors taking part. For example runners in a race will wear a prominent competition number so that they may be clearly identified from a distance.

In motorsport, competition numbers are attached to the vehicles taking part for identification. In some types of motorsport such as rallies, the competition number works in conjunction with special kinds of timing system (for example targa timing) and as a result numbers also usually relate to the competitors' due time and thus may exhibit gaps such as skipping from number 59 to number 100 (59 minutes to 1 hour due time).