Do optimistic expectations facilitate or hinder adaptive responses to relationship challenges? Traditionally, optimism has been characterized as a resource that encourages positive coping efforts within relationships. Yet, some work suggests optimism can be a liability, as expecting the best may prevent individuals from taking proactive steps when confronted with difficulties. To reconcile these perspectives, the current article argues that greater attention must be given to the way in which optimistic expectancies are conceptualized. Whereas generalized dispositional optimism may predict constructive responses to relationship difficulties, more focused relationship-specific forms of optimism may predict poor coping responses. A multi-method, longitudinal study of newly married couples confirmed that spouses higher in dispositional optimism (a) reported engaging in more positive problem-solving behaviors on days in which they experienced greater relationship conflict, (b) were observed to display more constructive problem-solving behaviors when discussing important marital issues with their partner in the lab, and (c) experienced fewer declines in marital well-being over the 1st year of marriage. Conversely, spouses higher in relationship-specific optimism (a) reported engaging in fewer constructive problem-solving behaviors on high conflict days, (b) were observed to exhibit worse problem-solving behaviors in the lab—particularly when discussing marital issues of greater importance—and (c) experienced steeper declines in marital well-being over time. All findings held controlling for self-esteem and neuroticism. Together, results suggest that whereas global forms of optimism may represent a relationship asset, specific forms of optimism can place couples at risk for marital deterioration.