Patients undergoing hematopoietic stem cell transplantation (HSCT) deal with numerous physical and psychological symptoms during acute hospitalization and recovery. Of the few psychosocial interventions tailored to the needs of the HSCT population, most focus on the needs of patients in the pre-transplant phase or during the HSCT hospitalization, but not during the acute recovery period starting at 100-days post-HSCT. Hence, the investigators developed a remotely-delivered positive psychology intervention, Positive Affect in the Transplantation of Hematopoietic Stem Cells (PATH). This intervention encourages patients to perform simple and enjoyable structured activities that increase the intensity of positive thoughts and emotions. With this multi-site randomized clinical trial, the investigators aim to find out whether PATH can improve psychological distress and quality of life in HSCT survivors, compared to usual care, using validated assessment tools.