The association between daily stress outside and inside of the relationship and marital functioning in the form of communication in conflict situations and marital quality was examined. We hypothesized that relationship stress mediates the association between external stress and marital functioning at the individual level, and that the association between relationship stress and marital quality is partially mediated by communication at the dyadic level. Using the Actor-Partner Interdependence and Common Fate Model, the results of 345 couples supported our hypotheses and revealed that a person's relationship stress is more strongly related with one's own external stress than with the partner's external stress. The findings indicate that both low relationship stress and a high level of positive communication are important in relationships.