OBJECTIVE: To better understand depression’s impact on family functioning from the perspectives of patients with major depressive disorder (MDD) and their partners; to develop and test patient and partner versions of a new self-reported measure, the Depression and Family Functioning Scale (DFFS), for use in clinical trials. METHODS: Concept elicitation interviews were conducted with 32 adults with clinician-diagnosed moderate-to-severe MDD and their respective partners. Twenty-six items were drafted to address relevant aspects of family functioning and were then tested and refined through two iterative sets of cognitive debriefing interviews, each conducted by the same pair of highly experienced researchers, including a licensed clinical psychologist. RESULTS: Depression negatively affects family functioning through poorer communication, increased conflicts, decreased family interaction, and decreased intimacy. No existing instrument measured all domains of interest, or had been rigorously developed and psychometrically validated in the target populations. The draft DFFS items generally tested well and only minor modifications were made to the items after the second set of interviews. Both patients and partners indicated that the final set of 15 DFFS items addresses all concepts of importance. CONCLUSIONS: The DFFS evaluates the impact of depression on family functioning and has the potential to provide important information that can facilitate a more comprehensive evaluation of new treatments in clinical trial settings. Although MDD severity was not confirmed with a standardized interview, in clinical practice in the US, MDD is generally not diagnosed with the use of a structured clinical interview or clinician-administered tool. In the current study, depression severity had little (if any) impact on the specific concepts elicited as being important to family functioning. In fact, patients with milder depression had more insight and were able to better articulate changes in family functioning with treatment.