Poole Harbour is a harbour in Dorset, southern England, with the town of Poole on its shores. The harbour is a drowned valley formed at the end of the last ice age and is the estuary of several rivers, the largest being the Frome. The harbour has a long history of human settlement stretching to pre-Roman times. The harbour is extremely shallow (average depth: 48cm), with one main dredged channel through the harbour, from the mouth to Holes Bay in Poole.

Once a major port, freight transport has declined, but the port is still served by regular cross-Channel passenger ferries. Coastal trading vessels are also frequent visitors, unloading various cargos on the quaysides at Hamworthy, and fleet of fishing vessels operates from the south end of Poole Quay. There is considerable leisure usage of the harbour, by a combination of yachts and other private craft, cruise boats that ply the harbour, and ferries that provide a passenger link to Brownsea Island. The harbour is managed by the Poole Harbour Commissioners (PHC).

Poole Harbour is one of several which lay claim to the title of the largest or second largest natural harbour in the world.

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