Sunitinib is an oral multikinase inhibitor that blocks the vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR) alpha and beta, c-kit, and other receptors. These attributes have proven to be efficacious in the treatment of metastatic renal cell carcinoma (RCC) and unresectable gastrointestinal stromal tumors (GIST). Most side effects, including hypertension, hand-foot syndrome, and diarrhea are generally well manageable. Clinical trials are underway to determine the efficacy of sunitinib in other tumor types including metastatic breast, colorectal, and lung cancers. This chapter will detail the preclinical data leading to the results of the pivotal phase III clinical trials that have led to the widespread use of sunitinib in metastatic RCC and advanced GIST.