St. Mary's High School is a secondary school in Calgary, Alberta, Canada. It is operated by the Calgary Catholic School District (CCSD). The school is well known in Calgary for its historical significance. It attracts significant numbers of students from throughout the city, even those closer to other Catholic high schools, who wish to take advantage of programs not offered in their local high school. Also, for some, it is a tradition to attend the same school as their parents and grandparents.