The WSOP is a series of online tournaments held annually in Las Vegas and, since 2004, sponsored by Caesars Entertainment Corporation (known as Harrah's Entertainment until 2010). It dates its origins to 1970, when Benny Binion invited seven of the best-known online players to the Horseshoe for a single tournament, with a set start and stop time, and a winner determined by a secret ballot of the seven players.