This chapter lays the groundwork for navigating psychological scholarship on gender, sex, and sexualities. It presents some central concepts in these fields, as well as tools for thinking about and asking questions about these concepts and their use. The chapter begins with a discussion of social categories and categorization and then moves to a focus on sex categories. Next is an examination of three concepts that psychologists employ with great frequency, but with varying and sometimes ambiguous meanings: gender, difference, and "the social." The closing section offers a series of questions to guide students as they read books and articles on gender, sex, and sexualities.