Phi Beta Sigma Fraternity, Inc. (ΦΒΣ) is a historically African American fraternity. It was founded at Howard University in Washington, D.C. on January 9, 1914, by three young African-American male students with nine other Howard students as charter members. The fraternity's founders, A. Langston Taylor, Leonard F. Morse, and Charles I. Brown, wanted to organize a Greek letter fraternity that would exemplify the ideals of Brotherhood, Scholarship and Service while taking an inclusive perspective to serve the community as opposed to having an exclusive purpose. The fraternity exceeded the prevailing models of Black Greek-Letter fraternal organizations by being the first to establish alumni chapters, youth mentoring clubs, a federal credit union, chapters in Africa and a collegiate chapter outside of the United States. It is the only fraternity to hold a constitutional bond with a historically African-American sorority, Zeta Phi Beta (ΖΦΒ), which was founded on January 16, 1920 at Howard University in Washington, D.C., through the efforts of members of Phi Beta Sigma.

The fraternity expanded over a broad geographical area in a short amount of time when its second, third, and fourth chapters were chartered at Wiley College in Texas and Morgan State College in Maryland in 1916, and Kansas State University in 1917. Today, the fraternity serves through a membership of more than 200,000 men in over 700 chapters in the United States, Africa, Europe, Asia, and the Caribbean. Although Phi Beta Sigma is considered a predominantly African-American fraternity, its membership includes college-educated men of African, Caucasian, Hispanic, Native American, and Asian descent. According to its Constitution, academically eligible male students of any race, religion, or national origin may join while enrolled at a college or university through collegiate chapters, or professional men may join through an alumni chapter if a college degree has been attained, along with a certain minimum number of earned credit hours.

Phi Beta Sigma is a member of the National Pan-Hellenic Council (NPHC) and a former member of the North American Interfraternity Conference (NIC). The current International President is Chris V. Rey, J. D., and the fraternity's headquarters are located at 145 Kennedy Street, NW, Washington, D.C.