Tampa Bay is a large, natural harbor and estuary along the Gulf of Mexico on the west central coast of Florida, comprising Hillsborough Bay, Old Tampa Bay, Middle Tampa Bay, and Lower Tampa Bay.

"Tampa Bay" is not the name of any municipality. This misconception probably stems from the naming of several professional sports franchises (including the Tampa Bay Buccaneers, Tampa Bay Lightning, Tampa Bay Rays, and FC Tampa Bay) whose names represent the collective Tampa Bay Area, the hub of which is the city of Tampa, Florida.

Approximately 6,000 years ago, Tampa Bay formed as a brackish drowned river valley typeestuary with a wide mouth connecting it to the Gulf of Mexico. Prior to that time, it was a large fresh water lake, possibly fed by the Floridan Aquifer through natural springs. Though the exact process of the lake-to-bay transformation is not completely understood, the leading theory is that rising seas levels following the last ice age coupled with the formation of a massive sink hole near the current mouth of the bay created a connection between the lake and the gulf.