Couple distress has a high prevalence as well as high comorbidity with a broad range of emotional, behavioral, and physical health problems. Marriage and relationship problems also influence individuals' response to treatment for a wide range of psychological disorders. Hence, clinicians need to be skilled in conducting clinical assessment involving relationships in order to provide effective interventions, whether working primarily with individuals, couples, or the broader family system. This article first introduces brief screening measures and clinical methods for diagnosing couple distress in clinical as well as research applications. It then conceptualizes and assesses couple distress for the purpose of planning and evaluating treatment. The article also reviews empirical findings regarding behavioral, cognitive, and affective components of couple distress, and specific techniques derived from clinical interviews, behavioral observations, and self-reports. Finally, it considers emerging technologies for assessing intimate relationships and makes recommendations for future research.