An extensive survey of the research literature on sexual orientation was undertaken for the purpose of determining how sexual orientation had been conceptually and operationally defined and how research subjects had been identified and selected. Two hundred-twenty-eight articles from 47 different journals were analyzed. Sexual orientation, it was found, was conceptually defined in 28 studies and operationally defined in 168. In 196 studies respondents were identified on the basis of the settings in which they were found. Because of the great variation in both conceptual and operational definitions, it was almost impossible to determine with certainty the theoretical frameworks used in the studies. The wide divergency in the definitions of sexual orientation, the investigators conclude, is symptomatic of an underlying conceptual confusion.