Willem de Vlamingh (born 28 November 1640, died ?) was a Dutch sailor who explored the southwest coast of Australia (then "New Holland") in the late 17th century.

In 1696 de Vlamingh's expedition left Amsterdam to chart the south-west coast of New Holland to aid navigation on the Indian Ocean route from African Cape. There were three ships under his command: the Geelvink, Nyptangh and the Wezeltje.

• On December 29 1696, he discovered Rottnest Island. He named the island from the number of rats (actually the native marsupial quokkas), observed.
• On January 10 1697, he discovered the Swan River. He named the river after the Black Swans which he observed in large numbers.
• On February 4 1697, he landed at Dirk Hartog Island, Western Australia, and replaced Dirk Hartog’s pewter plate with one bearing a record of both visits. The original plate is preserved in the Rijksmuseum.

De Vlamingh's name is preserved in the names of a number of geographical features in Western Australia.