In the early 21st century, it has become commonplace to encounter items about sexual orientation alongside race, gender, and age on the demographic questionnaires that typically begin or conclude [Page 1533]research surveys. Such questions may appear obvious, such as asking participants to check a box with categories such as gay, straight, bisexual, or “other.” But this kind of question is merely the first step in the complex transformation of individuals’ sexual selves into a research variable that can be manipulated, calculated, and used to compare individuals and groups for their similarities and more often differences. This entry examines some of the challenges associated with collecting sexual orientation information for research purposes and the potential for researcher bias that frequently arises in the process.