A tennis shirt, also called a polo shirt or a golf shirt, is a T-shaped shirt with a collar, two or three buttons down a slit below the collar, two small slits on the bottom of either side, and an optional pocket. The most common way to wear a tennis shirt is with the top button undone only and with an optional T-shirt underneath for warmth. Common fabrics for these shirts include pique cotton, jersey cotton, or pima cotton. The names for this type of shirt come from the sports they are associated with.

This type of shirt is made in several colors and patterns. Wide horizontal stripes are common, as are solid color shirts. Due to the outdoor nature of the sports they are associated with, the shirts are often colors associated with nature, such as brown, dark blue, green, and orange. Tennis style shirts are usually of brighter colors and often feature much more white. Tennis shirts can be little more than T-shirts with buttons to quite thick and substantial shirts for heavy wear.

Sometimes a tennis shirt's cloth is cut so that the back hangs a few centimeters lower than the front. This is called a tennis tail. The original 1929 design by tennis player Rene Lacoste called for a thick pique collar that one would wear turned up in order to block the sun from one's neck.

As is implied by the name, the tennis shirt is worn by tennis, polo, and golf players. This style is also worn by those merely associated to the sports by work, such as caddies, golf professionals , and sports announcers. It is also a favored shirt for those working outside, such as groundskeepers and construction workers due to its ruggedness. During the 1990's, the tennis shirt became the standard informal business attire for the high tech industry. In the People's Republic of China, most younger government officials wear a tennis shirt (sometimes made of silk) as standard business attire. In many schools with a uniform, especially junior schools, polo shirts are compulsary wear for both boys and girls. However,in almost every school, uniform or not, polo shirts are compulsary for PE (games or gym.)