The Firth of Tay is a firth on the east coast of Scotland, into which the River Tay empties. The firth is surrounded by four council areas: Fife, Perth and Kinross, City of Dundee, and Angus. Its maximum width is 3 mi.
Two bridges span the firth: the Tay Road Bridge and the Tay Rail Bridge.
The marshy Mugdrum Island is the only major island in the firth.
The Firth of Tay in Antarctica was discovered in 1892–93 by Captain Thomas Robertson of the Dundee whaling expedition and named by him after the one in Scotland. He also named nearby Dundee Island in honour of the main city on the firth.