This study develops and tests a theoretical model drawing on social psychological and resource-mobilization perspectives of social movement theory to explain changes in social movement participation and support for activism among Earthwatch Expedition volunteers. The social psychological perspective of social movements recognizes the role of self-efficacy and consciousness-raising for the participation in and success of social movement organizations. The resource mobilization perspective of social movements stresses rationality and the importance of funding and networks for the success of social movement organizations. Utilizing these two theoretical perspectives as my foundation, I hypothesize that participation in an Earthwatch Expedition increases volunteers' participation in social movement organizations in ways such as making monetary donations, voting with the organization's platform in mind, or attending rallies and marches. I also hypothesize that volunteers will increase their support for others who participate in these same types of activities. Earthwatch Expeditions are a form of alternative tourism in which volunteers participate in any of 126 different types of 10-14 day research-oriented expeditions that may include evaluating the health of a coral reef, studying maternal health among west African women, assessing the killer whale population off the coast of Puget Sound, or recording oral history in Dominica. I conducted pre- and post-trip surveys in June and July of 1998, resulting in 363 completed surveys. I analyzed data using multiple regression to discover relationships between pre-trip and post-trip measures of social movement participation, activism support, networks, self-efficacy, and consciousness-raising. In other words, I explored ways in which an alternative tourism experience like Earthwatch can change a person's ideas about their own social movement participation, the social movement activities of others, their perceived ability to overcome obstacles in order to implement social change, and their awareness of social issues. Results suggest that participation in an Earthwatch Expedition has a positive effect on volunteers' social movement participation, their awareness of social issues, their networks, and their ability to overcome obstacles, but little effect on activism support. / Ph. D.