The game was originally believed to have evolved from the original beer pong played with paddles which is generally regarded to have had its origins within the fraternities of Dartmouth College in the 1950s and 1960s, where it has since become part of the social culture of the campus. The original version resembled an actual ping pong game with a net and one or more cups of beer on each side of the table. Eventually, a version without paddles was created and the names Beer Pong and Beirut were adopted in some areas of the United States sometime in the 1980s.

Bucknell University's student-run newspaper, The Bucknellian, claims Delta Upsilon fraternity members at Bucknell created "Throw Pong", a game very similar to beer pong, during the 1970s. "Throw Pong" was then brought to Lehigh University by fraternity brothers who visited Bucknell and this led to the creation of the version of beer pong that is played today.

In some places, Beer Pong refers to the version of the game with paddles, and Beirut to the version without. However, according to a CollegeHumor survey, beer pong is the more common term than Beirut for the paddle-less game.

More Info: en.wikipedia.org