The Church of Scientology International (CSI) is a California non-profit corporation within the worldwide network of Scientology organizations. CSI is referred to as the "mother church" of the Church of Scientology, managing church growth and compliance with standards of the teachings of Scientology's founder, L. Ron Hubbard.

In a 1993 memorandum by CSI to the Internal Revenue Service about CSI's role and functions, its personnel and its income:

CSI [...] is the Mother Church of the Scientology religion, with ecclesiastical authority over the ministry of religious services to parishioners by all subordinate churches within the ecclesiastical hierarchy. This church has a staff of approximately 990 individuals and an annual budget of approximately $46.8 million, based on its annual disbursements for the most recent year for which financial statements are available."

The Church of Scientology International (CSI) was incorporated in California in 1981. As of 2023, CSI's principal address is 6331 Hollywood Boulevard, Los Angeles 90028, in the Hollywood Guarantee Building, one of the many Scientology properties. CSI also operates facilities at Gold Base in Gilman Hot Springs, California.

On September 21, 1993, the following Scientology officials held positions at CSI: the board of trustees was Mark Rathbun, Ray Mithoff, Mark Ingber, Marc Yager and John Eastment; the board of directors were Jens Uhrskov, Michael Rinder and Guillaume Lesèvre; Heber Jentzsch was the president, Brian Anderson was vice-president, Lynn Farny was secretary, Leslie Browning was assistant secretary and Jonathan Epstein was treasurer.

On August 18, 1993, CSI filed an application for tax exemption under section 501(c)3) of the Internal Revenue Code, and on September 3, 1993 a request for "group exemption" for all the affiliated Class V organizations. In the same year, the Internal Revenue Service (IRS) granted CSI's request for exemption.

The granting of tax exemption to CSI and other Scientology corporations was preceded by years of continuous litigation between the IRS and the various entities of Scientology. According to former high-ranking executives, the Scientology organization had launched about 200 lawsuits against the IRS until 1991. During the same time, individual parishioners of Scientology had initiated 2,300 claims against the agency, challenging the denial of tax deduction for their services at Scientology organizations. In 1991, the dispute over Scientology's tax-exempt status began to resolve through high-level meetings between David Miscavige and the then Commissioner of the IRS, Fred Goldberg, who encouraged a final resolution of the legal battle.

Within the corporate structure of the Scientology network, the Religious Technology Center owns the right to license the Scientology trademarks and service marks through a so-called "assignment agreement" between RTC and the founder of Scientology, L. Ron Hubbard on May 16, 1982.