The beliefs people hold about how relationships form, change, and develop predict how they will think, perceive, respond, and behave in romantic relationships from beginning to end. In this chapter, we review research on a particular set of implicit theories, termed destiny and growth beliefs. Destiny belief concerns the stability of one's impressions about romantic relationships and involves believing that relationships are either meant to be or they are not. Growth belief concerns the perceived stability of problems in the relationship and reflects the assumption that relationships can be maintained and problems can be overcome. These beliefs operate as fundamental assumptions about the nature of romantic relationships, and as such, they guide inferences about relationship experiences, and the ways people attempt to cope with relationship threats and challenges. We first provide a discussion of the conceptual origins of these beliefs. We then review measurement approaches and emerging themes, and discuss future directions for additional contributions to this literature.