Colonel By Secondary School is a high school in the Beacon Hill neighbourhood of Ottawa, Ontario, Canada. It is a non-semestered school, and was the only English public school in Ottawa that offers the International Baccalaureate (IB) diploma programme until Merivale High School began its IB programme in September 2019. Colonel By is renowned locally and provincially as an academically rigorous school. In the 2018–19 school year, it was ranked the sixth best secondary school in Ontario by the Fraser Institute.

Lieutenant-Colonel John By was an English military engineer. He is best known for having supervised the construction of the Rideau Canal and for having founded Bytown in the process. It developed and was designated as the Canadian capital, Ottawa.