For over two decades, resources have been assumed to be a fundamental determinant of the course and character of social movement organizations (SMOs) and their activities. Yet surprisingly little research evaluates this taken-for-granted assumption. Using data from ethnographic fieldwork on 15 homeless SMOs in eight U.S. cities, we construct an empirically grounded typology of resources and assess the combinations of resources necessary for the viability of homeless SMOs. We then examine the sources of support for these organizations, highlighting the influence of benefactor organizations on SMO viability and tactics. Employing qualitative comparative analysis, we identify three resource configurations among the viable SMOs and find that certain resource types contributed more than others to viability. Support from benefactors also ensured viability of these organizations without moderating their tactics. We explain the implications of these findings for understanding the roles that resources and sponsorship or patronage play in the careers of SMOs and the relevance of resources, sponsorship, and organization to social movements of the poor. early two decades after the flowering of the resource mobilization perspective on social movements, many of the perspective's assumptions have been assimilated as the routine and unstated grounds of much contemporary work (Zald 1992:327). One such taken-for-granted assumption is that resources are a sine qua non determinant of the course and character of social movement organizations (SMOs) and their activities. Indeed, no other assumption is so fundamental to the resource mobilization perspective and a plethora of derivative work. Yet there is little definitive understanding of several resource-related issues relevant to the dynamics of SMOs. One such issue concerns the conceptualization and identification of resources; a second issue addresses whether some types of resources are more important than others for mobilization and collective action; the third issue concerns resource derivation, particularly the relative importance of externally derived versus internally derived resources; and the fourth issue concerns the implications of external support for SMO viability and tactical actions. We address these four issues with data on 15 homeless SMOs in eight U.S. cities, and we explore the implications of our findings for a more nuanced understanding of social movements of the poor.