Professional Engineers Ontario (PEO; known until 1993 as the Association of Professional Engineers of Ontario, APEO) is the self-regulatory body that governs Ontario's 85,000 professional engineers, and sets standards for and regulates engineering practice in the province. It is "the licensing and regulating body for professional engineering in the province".

PEO was created on June 15, 1922. It has a statutory mandate under the Professional Engineers Act of Ontario to protect the public interest where engineering is concerned, and is also mandated with educating its members about latest research and best practices developments, and maintaining a Code of Ethics that puts the public interest first. Licensed professional engineers are identified by the P.Eng. after their names.

PEO consists of 36 chapters, each representing a different geographic area in Ontario. PEO is governed by a Council of 29 members, of which 17 are elected by the licence holders and 12 are appointed by the provincial government. The organization has collaborated with the Ontario Society of Professional Engineers since 1947 to recognize professional engineers in Ontario who have made outstanding contributions to their profession and their community through the Ontario Professional Engineers Awards (OPEA).