Poldhu is a small area in south Cornwall, England, UK, situated on the Lizard Peninsula; it comprises Poldhu Point and Poldhu Cove. It lies on the coast west of Goonhilly Downs, with Mullion 2 kilometres (1.2 mi) to the south and Porthleven 7 kilometres (4.3 mi) to the north. Poldhu means "black pool" in Cornish.

The site is famous as the location of Poldhu Wireless Station, Guglielmo Marconi's transmitter for the first transatlantic radio message on December 12, 1901 to Marconi's temporary receiving station on Signal Hill, St. John's, Newfoundland.

The station's fifty acre (200,000 m²) plot was bought in 1900 and construction work ran from October 1900 to January 1901, to a design by John Ambrose Fleming. The original 20 mast circular aerial was destroyed in a storm on September 17, 1901. For Marconi's experiments a temporary installation of two 200 foot (61 m) masts was used. The transmitter operated with a power of roughly 13 kW and a wavelength usually estimated at 170 meters.^{[citation needed]} The original mast layout was not rebuilt, it was replaced with a four mast design, 215 feet (66 m) high and forming a 200 foot (61 m) square.