Governments intend to meet resource constraints in professional palliative care by stimulating informal care, including volunteerism. However, little is known about current volunteer-professional collaboration. Such insights are relevant for future policy development regarding volunteer efficiency, quality of care, and the capacity of volunteer care to support health care services and professionals. To explore what constitutes volunteer-professional collaboration around palliative care. A qualitative study was conducted using semistructured focus groups with volunteers, nurses, psychologists, and family physicians and semistructured interviews with people with serious illnesses and with family carers. Participants were recruited from hospital, home-care, day-care, and live-in services in Flanders, Belgium. Interviews and focus groups were audio-recorded, transcribed verbatim, and analyzed by using a phenomenological approach. Two researchers coded independently in NVIVO 11 and reached a definitive coding scheme by comparing their resulting conceptual schemes. Seventy-nine people participated in the study. Volunteers collaborate mostly with nurses, less with psychologists but not with physicians. Volunteer-professional collaboration entails mutual information-sharing regarding patient conditions and coordination of care provision, whereas nurses and psychologists provide emotional and functional support for volunteers. Lack of access to nurses, of leadership, and of patient-information-sharing guidelines were the most prominent barriers to collaboration. Volunteers are at the front line of palliative care provision and therefore collaborate intensely with nurses, particularly in dedicated palliative care services. However, collaboration with other professionals is limited. The presence and availability of nurses was found to be crucial for volunteers, both for support and to achieve integration through collaboration.