A baseball cap is a soft cap with a round crown and a hard peak protruding at the front. The front of the hat usually contains the design or logo of the sports team (i.e. the name of the baseball team or related company, when used as a commercial marketing technology). The back of the hat can "fit" the size of the wearer's head, or it can have plastic, Velcro or elastic adjusters, so it can be quickly adjusted to fit different wearers. The baseball cap is part of the traditional uniform players wear, with the brim pointing forward to protect the eyes from the sun. Hats often appear in casual wear.

Baseball caps are made of various types of materials and have various styles that can be used for different purposes. Baseball players in major and minor leagues wear classic wool hats (or more recently polyester) with the team's simple logo and colors. The logo is usually embroidered on the fabric.

Once upon a time, baseball caps were standard size caps. Since 1980, they have also been available in an integrated form with adjustable straps on the back. This style, commonly known as "reversion", has become increasingly popular as a fashion accessory. Progress in textiles has led to the use of "elastic fit" hats, which use Lycra or rubber to give the hat a fit style while still "adjusting" its size.