Cell-based therapies are rapidly advancing as a promising approach for treating blood-based cancers and other unmet clinical needs. As the pace of development and commercialization of the therapies increases, regulatory scrutiny on the materials and processes used in their manufacturing intensifies. This chapter focuses on raw materials—also known as ancillary materials—that come into direct contact with the cell product during manufacturing but are not present in the final therapeutic product. Examples include: cell culture media, supplements, enzymes, cryopreservation agents, buffers, and antibodies. The selection and qualification of these materials are critical to ensuring the quality, safety, consistency, and efficacy of the final cell product. Raw materials vary in grade and composition, and their suitability for use in cell therapy manufacturing must be rigorously evaluated and continuously reassessed through a risk-based approach throughout clinical development. This chapter also examines the regulatory landscape for raw materials, noting the lack of specific regulations but highlighting guidance from key regional and international organizations. Given the variability in raw material quality and labeling, developers and suppliers need to collaborate closely to qualify materials for their intended use. The chapter concludes by outlining the regulatory considerations and risks involved in raw material selection, providing case studies that offer practical insights from real-world experiences.