Social movements interact in a wide range of ways, yet we have only a few concepts for thinking about these interactions: coalition, spillover, and opposition. Many social movements interact with each other as neither coalition partners nor opposing movements. In this article, I argue that we need to think more broadly and precisely about the relationships between movements and suggest a framework for conceptualizing noncoalitional interaction between movements. Although social movements scholars have not theorized such interactions, "strange bedfellows" are not uncommon. They differ from coalitions in form, dynamics, relationship to larger movements, and consequences. I first distinguish types of relationships between movements based on extent of interaction and ideological congruence and describe the relationship between collaborating, ideologically opposed movements, which I call "collaborative adversarial relationships." Second, I differentiate among the dimensions along which social movements may interact and outline the range of forms that collaborative adversarial relationships may take. Third, I theorize factors that influence collaborative adversarial relationships' development over time, the effects on participants, and consequences for larger movements, in contrast to coalitions. I draw on the case of the relationship between antipornography feminists and conservatives during the 1980s, charting the dynamics of their interaction across arenas and over time.Social movements interact in a wide range of ways, yet we have only a few concepts for thinking about these interactions: coalition, spillover (mutual influence without shared collective action), and opposition. The concept of coalition has come to carry excessive conceptual weight as the term for a wide range of relationships between movements. Many social movements interact with each other as neither coalition partners nor opposing movements. In this article, I argue that we need to think both more broadly and more precisely about the relationships between movements. In order to understand modes and consequences of collective action more fully, I suggest a framework for conceptualizing movements' interaction and analyze noncoalitional interaction between opposing movements. Although social movements scholars have not theorized such interactions, they are widely recognized with the colloquy "strange bedfellows" and are not uncommon (Smith 2008). They differ from coalitions in their forms, dynamics over time, relationship to larger movements, and consequences. Understanding their dynamics is intrinsically important, as is understanding coalitions or countermovements, for understanding specific social movements as well as the broader forces that influence movements' interactions with each other. Here, I draw on the case of the relationship between anti-pornography feminists and antipornography conservatives during the 1980s to conceptualize the dynamics of noncoalitional interactions and develop an analytical approach that may be applied more broadly.