Philip Moeller was an American stage producer and director, playwright and screenwriter, born in New York where he helped found the short-lived Washington Square Players and then with Lawrence Langner and Helen Westley founded the Theatre Guild.

The Washington Square Players (WSP) was a theatre troupe and production company that existed from 1915 to 1918 in Manhattan, New York City. It started as a semi-amateur Little Theatre then matured into a Repertory theatre with its own touring company and drama school. It received national newspaper coverage and sparked like-minded companies across the country. After it ceased operating, three of its members founded the Theatre Guild.