The Southern California Intercollegiate Athletic Conference was formed in 1915 when five Southern California institutions combined for the purpose of promoting and governing competition in intercollegiate sports with the fundamental principle of the conference being to encourage the highest ideals of amateur sports in an environment of high academic standards.

While the mission of the conference has remained intact since the beginning, the membership has varied over the years.  The conference stood at eight members from 1991-2011, and with the addition of Chapman University in 2011 now stands at nine.  The five original SCIAC schools are still members: California Institute of Technology, Occidental College, Pomona College, University of Redlands, and Whittier College. Occidental and Redlands are, however, the only ones to have uninterrupted membership.  They have since been joined by California Lutheran University, Claremont-Mudd-Scripps Colleges, and University of La Verne to comprise the current membership. (Pomona College now has become Pomona-Pitzer Colleges for athletics.)

The following is a chronology of the membership changes over the years:

1915 Caltech, Occidental, Pomona, Redlands and Whittier found SCIAC
1920 UCLA joins (then known as the Southern Branch of the University of California)
1926 La Verne College and San Diego State Teachers College join
1927 UCLA leaves
1931 UC Santa Barbara joins (then known as Santa Barbara State Teachers College)
1934 Caltech and Pomona leave
1938 UC Santa Barbara and La Verne leave; Caltech and Pomona rejoin
1939 San Diego State leaves
1943 Whittier leaves
1946 Whittier rejoins
1947 Pomona combines with Claremont Men's College for athletics (Pomona-Claremont)
1950 Chapman College begins competition as an associate in baseball, basketball and tennis
1952 Chapman's association ends
1958 Claremont combines with Harvey Mudd College for athletics (Claremont-Mudd) [they are ineligible for SCIAC titles this year]
1971 La Verne rejoins; Pomona combines with Pitzer College for athletics (Pomona-Pitzer)
1976 Claremont-Mudd combines with Scripps College for athletics (Claremont-Mudd-Scripps)
1991 California Lutheran University joins [ineligible for football title in 1991]
2011 Chapman University joins [ineligible for SCIAC titles in 2011-12 academic year]



The membership has varied between four and nine institutions. The following is a summary of which years had what number of members:
 

Membership
Number
  Years at
Membership Level
4 1943-1946 3
5 1915-20, 1939-43, 1946-58 21
6 1920-26, 1934-39, 1958-71 24
7 1927-31, 1971-91 24
8 1926-27, 1931-34, 1991- 24
9 2011