Roommate.com, LLC (defendant) operated a website where individuals could post information about themselves, including sex, sexual orientation, and familial status, to assist in their search for a roommate. The Fair Housing Councils of San Fernando Valley and San Diego (plaintiffs) brought suit, alleging among other things that Roommate.com’s website was discriminatory in violation of the Fair Housing Act (FHA). The FHA prohibits discrimination on the basis of "race, color, sex, familial status, or national origin" with respect to the rental or sale of a "dwelling." The FHA defines "dwelling," in turn, as "any building, structure, or portion thereof which is occupied as, or designed or intended for occupancy as, a residence by one or more families." The district court granted the plaintiffs' motion for summary judgment, finding that Roommate.com violated the FHA by prompting users to enter discriminatory preferences, matching users based on those preferences, and publishing the preferences. The district court enjoined Roommate.com from continuing those practices. Roommate.com appealed to the United States Court of Appeals for the Ninth Circuit.