A hair iron or hair tong is a tool used to change the arrangement of the hair using heat. There are three general kinds: curling irons, used to make the hair curly, straightening irons, commonly called straighteners or flat irons, used to straighten the hair, and crimping irons, used to create crimps of the desired size in the hair.

Hair straightening is a hair styling technique used since the 1890s involving the flattening and straightening of hair in order to give it a smooth, streamlined, and sleek appearance. It became very popular during the 1950s among black males and females of all races. It is accomplished using a hair iron or hot comb, chemical relaxers, Japanese hair straightening, Brazilian hair straightening, or roller set/blowdryer styling. In addition, some shampoos, conditioners, and hair gels can help to make hair temporarily straight.