Ridley College (also known as RC, Ridley) is a private boarding and day university-preparatory school located in St. Catharines, Ontario, Canada, 20 miles (32 km) from Niagara Falls. The school confers the Ontario Secondary School Diploma and the International Baccalaureate diploma programme. Ridley is one of the oldest private schools in Canada, and has the largest boarding program in Ontario, with students representing over 55 countries.

Established as an Anglican-affiliated all-boys school in 1889, Ridley became coeducational in 1973. The school is divided into ten houses, each of which serves as a residence and community for its students. All students take part in an extensive extracurricular program including sports (ranging from a beginner to varsity level), arts and theatre opportunities, student initiatives, and community service. Ridley's boarding program plays a dominant role in its curriculum, with faculty heavily involved in student life outside the classroom in roles such as housemasters, coaches, and advisors.

Ridley is a member of the Canadian Accredited Independent Schools, the Headmasters' and Headmistresses' Conference and competes in the Conference of Independent Schools of Ontario Athletic Association (CISAA) sports conference, of which it is one of four original founding schools. Ridley has an array of student clubs, many of which take part in both Canadian and international competitions. The school's overall curriculum emphasizes a balanced and disciplined combination of academics, athletics, school involvement, and community service. Ridley alumni are known as Old Ridleians, and are entitled to use the post-nominal letters "O.R."