Imatinib is a drug used to treat certain types of cancer. It is currently marketed by Novartis as GleevecŪ (USA) or GlivecŪ (Europe/Australia) as its mesylate salt, imatinib mesilate (INN). It is occasionally still referred to as CGP57148B or STI571 (especially in older publications). It is used in treating chronic myelogenous leukemia (CML), gastrointestinal stromal tumors (GISTs) and a number of other malignancies.

It is the first member of a new class of agents that act by inhibiting particular tyrosine kinase enzymes, instead of non-specifically inhibiting rapidly dividing cells.