Chemotherapy uses cytotoxic drugs that target rapidly dividing cells to kill cancer cells throughout the body. As a systemic treatment, it reaches primary tumors and metastatic sites alike, making it indispensable for hematological malignancies and widespread solid tumors. Chemotherapy may be curative — as for lymphoma, testicular cancer, and leukemia — or used neoadjuvantly to shrink tumors before surgery, adjuvantly to eliminate microscopic residual disease, or palliatively to control symptoms. Modern supportive care has transformed the tolerability of chemotherapy, with effective antiemetics, growth factors, and individualized dosing strategies.