Marriage and other long-term committed relationships are an integral part of our lives and confer many benefits. Unfortunately, many couples experience significant relationship distress and about half of marriages end in divorce. Among those who stay married, a notable number of couples remain in stably, severely distressed marriages for years or even decades. Given the serious physical and psychological consequences of relationship distress and divorce for spouses and their children, it is clear that relationship science––the basic and applied study of relationship development, maintenance, and dysfunction––is of critical importance.The Oxford Handbook of Relationship Science and Couple Interventionsshowcases cutting-edge research in relationship science, including couple functioning, relationship education, and couple therapy. The book begins with the most current definitions of and classifications for relationship dysfunction, which are reflected in the most recent versions of theDiagnostic and Statistical Manual of Mental Disorder (DSM-5)and theInternational Classification of Diagnoses (ICD-11). Next, the latest research on the biological, psychological, and interpersonal causes and correlates of couple dysfunction and subsequent treatment implications is presented. The latest findings regarding empirically supported prevention and treatment interventions for couple dysfunction are then presented, and diversity and cultural issues are discussed in the context of working with couples. The information contained in this handbook will benefit researchers who seek to understand relationship distress and design interventions to prevent and treat couple distress, and clinicians who are diagnosing, assessing, and treating couple dysfunction in their practices.