The Palk Strait is a strait that lies between the Tamil Nadu state of India and the island nation of Sri Lanka. It connects the Palk Bay to the northeast (and thence the Bay of Bengal) with the Gulf of Mannar to the south. The strait is wide. Several rivers flow into it, including the Vaigai River of Tamil Nadu. The strait is named after Robert Palk, who was a governor of Madras Presidency (1755-1763) during the British Raj period.

It is studded at its southern end with a chain of low islands and reef shoals that are collectively called Adam's Bridge (or the original name Rama's Bridge). This chain extends between Dhanushkodi on Rameswaram in Tamil Nadu and Talaimannar in Mannar in Sri Lanka. The island of Rameswaram is linked to the Indian mainland by the Pamban Bridge.

The shallow waters and reefs of the strait make it difficult for large ships to pass through, although fishing boats and small craft carrying coastal trade have navigated the strait for centuries. Large ships must travel around Sri Lanka. Construction of a shipping canal through the strait was first proposed to the British government of India in 1860, and a number of commissions have studied the proposal up to the present day. The most recent study of the Sethusamudram Shipping Canal Project, as it is now called, was an environmental impact assessment and a technical feasibility study commissioned by the Tamil Nadu government in 2004.

Like the English Channel, the Palk Strait has been taken up as a challenge by many long-distance swimmers.

The Indian epic poem Ramayana, written thousands of years ago in Sanskrit and an important Hindu text, recounts how Rama, with the help of an army of vanaras, built a bridge of stones across the sea to Lanka to rescue his wife Sita from the Asura king Ravana. The Ram Karmabhumi movement, encouraged by a NASA satellite photograph which they say proves that remnants of this bridge still exist, was formed to prevent the shipping canal from being built.

The name Adam's Bridge is a later play than Rama's bridge and derives from the story that South India or Sri Lanka was the site of the biblical earthly paradise, and that Adam's Bridge was created when Adam was expelled from paradise.