The theoretical agnosticism of family-based treatment (FBT) has precluded a thorough understanding of treatment mechanisms. We examined clinician and researcher perspectives on the mechanisms of FBT. Thirty-eight clinicians/researchers who had recently published in the domain of anorexia nervosa (AN) indicated their opinions as to the mechanisms of FBT, and content analysis was performed to identify relevant themes. Parental input was deemed crucial for weight-based symptom remission, and weight restoration was deemed crucial for cognitive symptom relief. Participants reported that mechanisms of FBT may be nullified by psychiatric comorbidities (50%), inappropriate weight goals (37%), or a long illness duration (24%). Attributions of causality to parents (66%) or family system factors (37%) were noted in instances of nonsuccessful outcomes. These findings offer important insights into clinician/researcher perspectives on the mechanisms of FBT and highlight beliefs among clinicians and researchers that may not reflect emerging evidence, or the theoretical framework of FBT.