The Philolexian Society of Columbia University is one of the oldest college literary and debate societies in the United States, and the oldest student group at Columbia. Founded in 1802, the society aims to "improve its members in Oratory, Composition and Forensic Discussion." The society traces its roots to a collegiate literary society founded in the 1770s by Alexander Hamilton, then a student at Columbia College, and was officially established by Hamilton's son, James Alexander Hamilton (Columbia College Class of 1805).

Philolexian (known to members as "Philo," pronounced with a long "i") has been called the "oldest thing at Columbia except for the College itself," and it has been an integral part of Columbia from the beginning, providing the institution with its distinctive color, Philolexian Blue (along with white, from her long-dispatched rival, the Peithologian Society).

Philolexian is one of many collegiate literary societies that flourished at the nation's early colonial colleges. Before fraternities, publications, and other extracurriculars became common, these groups—which generally bore Greek or Latin names—were the sole source of undergraduate social life.

Columbia's first such society was formed in the 1770s when the school was still known as King's College; among this unnamed organization's members was future Treasury Secretary Alexander Hamilton (Class of 1778) and his roommate Robert Troup. After the Revolution, a similar group known as the Columbia College Society for Progress in Letters was formed; among its members were John P. Van Ness (Class of 1789), later mayor of Washington, D.C., and Daniel D. Tompkins (Class of 1795), vice president of the United States under James Monroe. The group became extinct in 1795.

Building on these earlier efforts, Philolexian was established on May 17, 1802. Among its earliest members were future Columbia president Nathaniel Fish Moore (Class of 1802), and Alexander Hamilton's son, James Alexander Hamilton (Class of 1805), U.S. Attorney for the Southern District of New York. To accommodate freshmen, who were initially ineligible for admission, the Peithologian Society was formed four years later. For most of the next 100 years, Peithologian would serve as Philolexian's primary literary rival.

For most of the 19th century, Philo engaged in a wide range of literary activities, including debates within and without the society, essay writing, correspondence, and hosting speeches by eminent men of the city. In 1852, at the organization's semi-centennial celebration, alumni raised a prize fund of over $1,300 to endow annual awards in three categories: Oratory, Debate, and Essay. (The awards were eventually combined into a general "Philolexian Prize" which, since the 1950s, has been awarded annually by Columbia University's English department.)

During Columbia College's tenure in midtown Manhattan from 1857 to 1896, Philolexian often held their meetings in an old paper factory in the northeast corner of the 49th street campus.

In the 20th century, Philo broadened its range of activities as it became a training ground for essayist Randolph Bourne (Class of 1912), poet A. Joyce Kilmer (Class of 1908), and statesman V.K. Wellington Koo (Class of 1909), all prize winners in their time at Philo. In 1910 the society took a decidedly dramatic turn when it commenced a 20-year stretch of annual theatre productions, ranging from Elizabethan comedies to contemporary works. Many of the older productions, by the likes of Ben Jonson, Nicholas Udall, and Robert Greene, were North American debuts. Oscar-winning screenwriter Sidney Buchman (Mr. Smith Goes to Washington, Here Comes Mr. Jordan, Cleopatra) (Class of 1923) got a start playing Shakespeare's Richard II for a Philo production.