This study examined the psychometric equivalence of paper-and-pencil and Internet formats of key questionnaires used in couple research. Self-report questionnaires assessing interpersonal constructs (relationship satisfaction, communication/conflict management, partner support, emotional intimacy) and intrapersonal constructs (individual traits, psychological symptoms, contextual influences) were administered to young adults in committed dating relationships. The same measures were administered twice via paper-and-pencil and/or Internet methods over a 2-week period. Method order was counterbalanced among participants, and temporal stability was controlled. Intrapersonal and interpersonal measures generally remained reliable when administered online and demonstrated quantitative and qualitative equivalence across methods. The implications of online administration of questionnaires are discussed, and specific recommendations are made for researchers who wish to transition to online data collection. (Contains 4 tables.)