A baseball cap is a type of soft cap with a long, stiff bill that may either be curved or flat. The back of the cap may have a plastic, Velcro, or elastic adjuster so that it can be quickly adjusted to fit different wearers.

While the baseball cap is specifically associated with those who play the game of baseball, it is often worn as a fashion statement as well as semi practical headgear. It is very popular in the United States and Japan. Traditionally, the bill is worn forward, shielding the eyes from the sun, but it is also often worn backwards or at other angles. People with long hair in a ponytail may pull it through the gap in the cap above the adjustor.

Another version of the baseball cap is a plastic mesh cap with a foam front imprinted with a company logo. This style of baseball cap is sometimes called a trucker cap or a "gimme cap" because it is given away for free as an advertising pitch.

Wearing a baseball cap with the peak facing in a certain direction may denote membership in a gang. For this reason, some public schools ban baseball caps. The idea of wearing the cap backwards is commonly attributed to catchers in baseball, as when they began using facemasks, they had to turn the cap around to fit the mask on. It can also be found in professional tennis. Another profession associated with the wearing of a baseball cap backwards is that of photographer, notably paparazzi - for the reason that an SLR camera cannot be held vertically to the eye whilst wearing a baseball cap with the peak forwards.