BACKGROUND: When children are seriously ill, parents rely on communication with their clinicians. However, in previous research, researchers have not defined how this communication should function in pediatric oncology. We aimed to identify these communication functions from parental perspectives. METHODS: Semistructured interviews with 78 parents of children with cancer from 3 academic medical centers at 1 of 3 time points: treatment, survivorship, or bereavement. We analyzed interview transcripts using inductive and deductive coding. RESULTS: We identified 8 distinct functions of communication in pediatric oncology. Six of these functions are similar to previous findings from adult oncology: (1) building relationships, (2) exchanging information, (3) enabling family self-management, (4) making decisions, (5) managing uncertainty, and (6) responding to emotions. We also identified 2 functions not previously described in the adult literature: (7) providing validation and (8) supporting hope. Supporting hope manifested as emphasizing the positives, avoiding false hopes, demonstrating the intent to cure, and redirecting toward hope beyond survival. Validation manifested as reinforcing “good parenting” beliefs, empowering parents as partners and advocates, and validating concerns. Although all functions seemed to interact, building relationships appeared to provide a relational context in which all other interpersonal communication occurred. CONCLUSIONS: Parent interviews provided evidence for 8 distinct communication functions in pediatric oncology. Clinicians can use this framework to better understand and fulfill the communication needs of parents whose children have serious illness. Future work should be focused on measuring whether clinical teams are fulfilling these functions in various settings and developing interventions targeting these functions.