The Assembly of Catholic Bishops of Ontario is the association of the Catholic bishops in the Province of Ontario in the service of Catholics of Ontario.

By its very nature, the ACBO is a forum where the Bishops of Ontario reflect together and collaborate on projects to proclaim, celebrate and live the Good News of Jesus Christ in our province. It is an instrument of the collegiality that binds Bishops with each other under the leadership of the Bishop of Rome in a common purpose, a common mission, a common faith.

The ACBO is one of four regional assemblies of the Canadian Conference of Catholic Bishops, which is located in Ottawa. The CCCB is the national association of all Catholic bishops of Canada.