Alpha Phi Omega (ΑΦΩ), commonly known as APO, but also A-Phi-O and A-Phi-Q, is a coeducational service fraternity. It is the largest collegiate fraternity in the United States, with chapters at over 350 campuses, an active membership of over 25,000 students, and over 500,000 alumni members. There are also 250 chapters in the Philippines, one in Australia and one in Canada. The 500,000th member was initiated in the Rho Pi chapter of Alpha Phi Omega at the University of California, San Diego.

In North America, fraternities and sororities are social organizations at colleges and universities. They are sometimes collectively referred to as Greek life. Generally, membership in a fraternity or sorority is obtained as an undergraduate student but continues thereafter for life. Some accept graduate students as well. Individual fraternities and sororities vary in organization and purpose, but most share five common elements:Secrecy Single-sex membership Selection of new members based on a two-part vetting and probationary process known as rushing and pledging Ownership and occupancy of a residential property where undergraduate members live A set of complex identification symbols that may include Greek letters, armorial achievements, ciphers, badges, grips, hand signs, passwords, flowers, and colors