St Leonards School is a co-educational private boarding and day school for pupils aged 4–19 in St Andrews, Fife, Scotland. Founded in 1877 as St Andrews School for Girls Company, it adopted the St Leonards name upon moving to its current premises, the site formerly occupied by the University of St Andrews’ St Leonard's College, in 1883.

The school emerged from the St Andrews Ladies' Educational Association which was established in 1868. One of the school's founders was Lewis Campbell, chairman of the college council for many years and a Classics professor at St Andrews University who advocated for higher education for women. Consequently, from its earliest days, the college's senior students were encouraged to prepare to matriculate and enjoyed close links with various courses offered at the University of St Andrews; in 1892, the Fifeshire Journal asked its readers: "Who is to enjoy the proud distinction of being the first matriculated girl-student of St Andrews?" St Leonards remained an all-girls school until 1999, upon which it became fully co-educational. As an IB World School, St Leonards offers the International Baccalaureate's Primary Years, Middle Years, Career-related and Diploma programmes alongside the English-system GCSE/IGCSE. It is one of only two schools in Scotland to teach an IB curriculum throughout.

The school was established in 1877 by the St Andrews School for Girls Company whose Articles of Association were drawn up on the lines of Bristol's Clifton College, the public school for boys. The school's administrative and commercial ventures utilised the company's name until at least 1894. Madeline Daniell, the educationalist and campaigner for women's right to higher education, was one of two founding secretaries of the Company.

Dame Louisa Lumsden was appointed the School's first Headmistress in 1877. The belief of the school was that "a girl should receive an education that is as good as her brother's, if not better" and Lumsden was "determined to establish a veritable Eton for girls". Although her role as principal ended in 1882, her connection to the school remained strong for "forty-five years": During her time as a member of staff of the University of St Andrews' University Hall and in the years after, "Miss Lumsden returned many times to St Leonards to give lectures".

The school was, until 1894, operating primarily as a senior school, the junior school remaining informally structured until after that date.

In 1884, ground was feued [granted] from the University of St Andrews to the school which had also commenced the lease of a field from the university for recreational use. In 1894, Old Tom Morris laid out a 9 hole golf course for the girls at St Leonards.

To ensure that the teaching of Chemistry to the girls at the school was rigorous, in 1885, Dame Frances Dove, the principal, employed Thomas Purdie, Professor of Chemistry at St Andrews University as an external examiner for the school's senior students. From its earliest decades, the school's sixth formers "had the pleasure of attending lectures" in various subjects including Political Economy and Music at the University of St Andrews whilst others attended the university's Gifford Lectures.

In 1999, St Leonards Sixth Form and St Katharines Prep School opened their doors to boys for the first time; the school soon became completely co-educational.