The purpose of these studies was to develop and validate a measure of beliefs about sexual orientation (SO) that incorporates essentialist, social constructionist, and constructivist themes. The Sexual Orientation Beliefs Scale (SOBS) is offered as a multidimensional instrument with which to assess a broad range of beliefs about SO, which evidence suggests are highly correlated with positive and negative attitudes about sexual minorities. An initial exploratory factor analysis (EFA) was conducted in the general population with a lesbian, gay, bisexual, and transgender-identified (LGBT) sample (n = 323) and suggested a 4-factor structure of naturalness (α = .86), discreetness (α = .82), entitativity (α = .75), and personal and social importance (α = .68); this 4-factor structure was supported by confirmatory factor analysis (CFA) with an independent LGBT sample (n = 330; “Form 1”). Additional EFA (n = 183) and CFA (n = 201) in a college student, mostly heterosexual-identified population suggest a slightly different factor structure, whereby group homogeneity (α = .84) and informativeness (α = .77) are salient themes (“Form 2”), and this structure was replicated across SO groups. Finally, a study of test–retest reliability in an undergraduate, mostly heterosexual-identified sample (n = 45) demonstrated strong temporal stability for the SOBS.