Patient-reported outcomes (PROs) to measure quality of life (QOL) and other symptoms play an increasingly important role in clinical trials and regulatory approvals for hematopoietic cell transplantation (HCT) and chimeric antigen receptor T-cell (CAR-T) therapy. However, their adoption has been hindered by wide heterogeneity in the choice of PRO measures for clinical research, including the Functional Assessment of Cancer Therapy Bone Marrow Transplantation (FACT-BMT) and the European Organization for Research and Treatment of Cancer Quality of Life Core Questionnaire (EORTC QLQ-C30) inventories. Additionally, the potential for PRO integration into routine standard-of-care (SOC) practice for patients undergoing HCT or CAR-T therapy has not yet been realized. As part of a coordinated effort by three American Society for Transplantation and Cellular Therapy (ASTCT) Special Interest Groups, we developed best practices for PRO integration in adult and pediatric recipients of HCT and CAR-T therapy. We strongly encourage the use of Patient-Reported Outcomes Measurement Information System (PROMIS) or PRO version of Common Terminology Criteria for Adverse Events (PRO-CTCAE) instruments as the primary PRO measures for most HCT and CAR-T trials. Measures such as the PROMIS-29 inventory can be used for QOL assessments, while PRO-CTCAE item banks can be used for specific symptoms. Rationales for our strong recommendation to move from FACT-BMT and EORTC QLQ-C30 to PROMIS/PRO-CTCAE instruments include: (1) free licensing and ease of implementation, including in electronic medical records; (2) psychometric validation in a variety of oncologic settings, including during inpatient hospitalizations; (3) translation into multiple languages, with validation in both adult and pediatric settings; and (4) adoption into centrally-collected PRO protocols from the Center for International Blood and Marrow Transplant Research for both HCT and CAR-T recipients. Steps to operationalize these PRO measures are discussed, as are methods to migrate existing data from legacy PRO instruments. We similarly recommend the consideration of PRO integration into SOC clinical practice, including the development of threshold-based workflows to both personalize and standardize care in this setting. Other panel recommendations include the use of standardized timepoints for longitudinal PRO assessments and the inclusion of patient advocates when implementing PRO measures. Implementing these steps will improve the ability of PROs to improve outcomes for patients undergoing HCT or CAR-T therapy, both in trials and - more importantly - in SOC practice.