Onconephrology focuses on management of kidney disease in cancer, which manifests itself in a proteinuria, and electrolyte disorders. Many of these syndromes result from cancer treatments including chemotherapy, immunotherapy, chimeric antigen receptor T cells, and stem cell transplant. Others are due to kidney-specific effects of the cancer, as seen with monoclonal gammopathy or glomerular diseases associated with malignancy. Further, cancer risk itself is heightened in patients erations. In this installment of AJKD's Core Curriculum in Nephrology, we review these and other core concepts in onconephrology, using a case-based approach to highlight clinical decision making.