There are many drug interactions in pediatric oncology—between chemotherapy drugs themselves and chemotherapy drugs with adjuvant therapy. Since drug interaction in pediatric oncology is a subject for a whole book, this chapter is a guideline to understand and to find drug interactions when prescribed, and it does not list the drug interactions. For complete information about drug interactions in pediatric oncology, see the book Drug Therapy and Interactions in Pediatric Oncology: A Pocket Guide (Springer), which is given in the reference list of this book. To identify drug interactions, you need to correlate: These six subjects are explained below. Do not forget to also correlate antibiotics, support drugs, and all drugs that the child is receiving.