The 21 Club is an informal student organization at Princeton University. Memorials in the Princeton Alumni Weekly dating back to the class of 1953 mention membership in the 21 club [559], and it is likely that the club's formation was decades before this.

Although the 21 Club claims to predate many of the eating clubs at Princeton, it has become closely intertwined and associated with them. Membership in the club is ostensibly an open pass to any of the eating clubs [560].

It ostensibly draws its name from the number of members (21) that are inducted into the club every year, with Senior members of the club select, or tap, a Junior to receive their bid to the club each winter. However, current membership consists of 5 members each from four of the bicker clubs, (University Cottage Club, Ivy Club, Tiger Inn, and Cap and Gown Club) and a final member being an independent (not associated with any particular eating club).

One of the club's more notable alumni is James Baker, who described the club as having a mission similar to that of the Right Wing Club, "so named because we spent much of our time using our right arms to hoist spirituous beverages" [561].