Partner concurrency (i.e., overlapping sexual partnerships) facilitates the spread of STDs, including HIV. The present study explored the context of and motivations for partner concurrency among patients recruited from an urban STD clinic. Eight focus groups were conducted with 59 patients (47% women; 77% African American). Qualitative analyses revealed five motivational themes related to the occurrence of concurrent partnerships for men and women. Participants reported these partnerships tend to occur: when people believe that sexual partners are unfaithful or cannot be trusted; when sexual satisfaction is low; when patients report the need for different partners to fulfill multiple needs; in retaliation for a partner's concurrency; and when people wish to maintain a sexual relationship with an ex-partner who is the parent of a shared child. Four additional themes unique to men were identified. Men reported that they had multiple partners because this practice supports their sense of masculinity and is consistent with familial modeling and community norms, and because having multiple partners is "in a man's nature." Men also mentioned that the imbalance in the number of women-to-men in their sexual network facilitates partner concurrency. These findings can help prevention practitioners and researchers to develop interventions to reduce risk associated with partner concurrency.