Couple therapy research affirms that various approaches to couple treatment produce statistically and clinically significant improvement for a substantial proportion of couples in reducing overall relationship distress. Recent studies have extended these findings in indicating the effectiveness of couple-based interventions for a broad range of coexisting emotional, behavioral, or physical health problems in one or both partners. In contrast to these encouraging results, research also indicates that a sizeable percentage of couples fail to achieve significant gains from couple therapy or show significant deterioration afterward. Research on processes of change and predictors of treatment outcome in couple therapy provides preliminary evidence regarding factors potentially contributing to variable treatment response. The chapter concludes with 12 recommendations regarding future directions in couple therapy research and clinical training.