This is a competitive renewal application for training grant support in pediatric oncology. The goal of this T32 program is to train physicians who will be the future academic leaders in basic and/or clinical pediatric oncology research and who will work to reduce the burden of cancer in the pediatric population. To accomplish this goal we have engaged a diverse and outstanding training faculty that embraces multiple areas of basic ("wet bench"), translational and clinical research. This experienced and highly accomplished group includes members of the Department of Pediatric Oncology at the Dana-Farber Cancer Institute (DFCI), the Division of Pediatric Hematology/Oncology at Boston Children's Hospital (BCH), and additional components of the Harvard Medical School (HMS). Particular emphasis is placed on close mentorship of trainees in the selection of mentors and in on-going oversight during their research. The T32 program provides training in oncology research at the postdoctoral level for 8 trainees, selected from the combined DFCI-BCH pediatric hematology/oncology fellowship program, who are in their second, third and fourth years of training. The program is committed to identifying and supporting the most promising fellows, including minority candidates. Over the past 45 years the DFCI-BCH fellowship program has trained over 200 individuals, many of whom are leaders of academic pediatric hematology/oncology programs. Continued T32 support will ensure the training of investigational pediatric oncologists, whose research will contribute immeasurably to the understanding and management of childhood cancers.