Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a category of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents) as part of a standardized chemotherapy regimen. Chemotherapy may be given with a curative intent (which almost always involves combinations of drugs), or it may aim to prolong life or to reduce symptoms (palliative chemotherapy). Chemotherapy is one of the major categories of the medical discipline specifically devoted to pharmacotherapy for cancer, which is called medical oncology.

By common usage, the term chemotherapy has come to connote the use of rather non-specific intracellular poisons, especially related to inhibiting the process of cell division known as mitosis, and generally excludes agents that more selectively block extracellular growth signals (i.e. blockers of signal transduction). To avoid these connotations for recently developed (against specific molecular or genetic targets) therapies which inhibit of growth-promoting signals coming from classic endocrine hormones (primarily estrogens for breast cancer and androgens for prostate cancer) is known as hormonal therapy, while the inhibition of other growth-promoting influences (especially those associated with receptor tyrosine kinases) is known as targeted therapy.