A school uniform is an outfit—a set of standardized clothes—worn primarily for an educational institution. They are common in primary and secondary schools in many nations.^[where?] When used, they form the basis of a school's dress code.

Traditionally, school uniforms have tended to be subdued and professional. Boys' uniforms often consist of dark short or long trousers and light-colored shirt, often with a tie. Girls' uniforms vary greatly between countries and schooling systems, but typically consist of a dress or a blouse worn either with a skirt or culottes or under a pinafore. In some countries, gender-specific uniforms have been a point of contention, with some schools permitting female students to choose either skirts or trousers while still requiring male students to wear trousers. The use of a blazer or suit-like jacket for either gender is also fairly common, especially in countries with relatively cold weather. In some countries, such as Japan, school uniform is essentially standard in all schools using it, but in others, such as Great Britain, each school has an individual uniform, varying in colour and often making use of badges.