Key Biscayne is an island located in Miami-Dade County, Florida, United States, between the Atlantic Ocean and Biscayne Bay. It is the southernmost of the barrier islands along the Atlantic coast of Florida, and lies south of Miami Beach and southeast of Miami. The Key is connected to Miami via the Rickenbacker Causeway, originally built in 1947.

The northern portion of Key Biscayne is home to Crandon Park, a county park. The middle section of the island consists of the incorporated Village of Key Biscayne. The southern part of the island is in Bill Baggs Cape Florida State Park, and is adjacent to Biscayne National Park, one of the two national parks in Miami-Dade County.