Agincourt Collegiate Institute (known locally as ACI or Agincourt), formerly known as Agincourt High School and Agincourt Continuation School is a secondary school in Toronto, Ontario, Canada. It is located in Agincourt, a neighbourhood in the former suburb of Scarborough. It was owned and operated by the Scarborough Board of Education prior to it being amalgamated into the Toronto District School Board in 1998.

A.C.I. is one of the oldest surviving secondary high schools in the former Scarborough in the north, the other being R. H. King Academy (formerly known as Scarborough High School/Collegiate Institute) in the south.