This dissertation examines attitudes on same-sex marriage and how personal predispositions toward support and the climate of opinion interact to help create attitudes. Over the past few decades, support for gay rights has increased dramatically in the United States and many other countries around the world. I argue that, while the set of basic personal determinants of attitudes toward homosexuality and gay rights stays roughly the same, the impact of such determinants changes over time and space. The framework used in this dissertation draws on attitudinal and political psychology, political sociology and theories of contextual effects. I argue that over the course of their lives, people develop an overall propensity to tolerate or approve of homosexuality and support gay rights based on their political and social characteristics, such as religiosity, partisan or ideological identities, personality characteristics and various demographic characteristics (e.g., education, race, gender and age). The influence of these predispositions on gay rights attitudes is moderated by the political and social environments in which people live. Even among people whose predispositions push them consistently toward support for gay rights, if they live in a homophobic environment, support for gay rights will be attenuated compared to a similar individual living in a more socially tolerant environment.