Dartmouth House is a Georgian house in Mayfair, central London, England. It now serves as the headquarters of the English-Speaking Union (ESU), an educational charity. It is located at 37 Charles Street, southwest of Berkeley Square.Over 40,000 people use the building each year. The original building was constructed in the mid 18th-century; what today comprises Dartmouth House was two separate residences, numbers 37 and 38 Charles Street. The first owner of number 37 was Henry Herbert, 2nd Earl of Carnarvon, from 1757–1776.