The modern baseball cap that we know and love can be traced all the way back to the late 1800's, when the Excelsiors of Brooklyn began wearing caps along with their uniforms. Of course, real baseball cap history is often believed to have begun a little more recently, in the 1940's. It was during this timeframe that latex rubber was added to the materials that comprised the hats, stiffening and shaping them into the earliest ancestors of the baseball caps that are so familiar today.
Baseball caps were very ingeniously designed, despite their somewhat common appearance today. The addition of the bill or brim to the front of the baseball cap was probably secured their place on the heads of baseball players the world over and in history books around the globe. This stiff protuberance is designed to shield the eyes of baseball players (and anyone else who wears them) from the harsh rays of the sun. Originally, the bill of the hat was much shorter, and before the addition of rubber and other stiffening materials, it was much less structured. In fact, the earliest baseball caps had bills that more resembled those found on old-fashioned bonnets than the ones that we are familiar with today. In addition to being a useful tool to protect players'eyes from the potentially blinding rays of the sun, baseball caps were (and still are) used as a method of easily discerning which players belong to which teams. Indeed, they are generally colorized in a manner that matches the rest of the team's uniform, and often also display the teams' logo as well.
Despite their name baseball caps have evolved from being primarily utilized in baseball uniforms to being used in a whole host of other uniforms as well. Several branches of the armed forces utilize baseball caps as part of their uniforms, depending on the occasion. In addition, many private companies have also incorporated baseball caps into their uniforms.
Finally, the most modern portion of baseball cap history sees these familiar caps being incorporated into many wardrobes, both for utility and fashion purposes. They are easily customizable, and therefore make it easy for any person to advertise their own personal philosophy right on their own forehead.