See also Crown Cork

Bottle caps are small circular pieces of metal with plastic backings that are used to seal glass bottles, typically those containing soda and beer. For plastic bottles, a plastic bottle cap is used instead. A bottle cap is typically colorfully decorated with the logo of the brand of beverage.

Bottle caps were originally designed to be pressed over and around the top of the glass bottle to grab a small flange on the bottle. To open these bottles, a bottle opener is required. An innovation was the twist-off bottle cap that is pressed around screw threads instead of a flange. Such a bottle cap can be taken off merely by twisting the cap. Even though this is now the predominant form of bottle cap, non-twist-off caps are used by some manufacturers.

Bottle caps are also a way for bottlers to hold promotions, especially for soda companies. A message is printed on the inside of the cap and people with the right message may win a prize. Since the bottle must be purchased to determine the message and win, people usually purchase more of the drink to increase their chances of winning. The most common prize is a free soda from that company.

Some companies, such as Snapple, also print interesting facts on the inside of their caps. Usually this is done on wide-mouthed bottles that have large caps with enough printing area to put a small sentence.