In chemistry, a mesylate is any salt or ester of methanesulfonic acid (CH₃SO₃H). In salts, the mesylate is present as the CH₃SO₃^- anion. When modifying the International Nonproprietary Name of a pharmaceutical substance containing the group or anion, the correct spelling is mesilate (as in imatinib mesilate, the mesylate salt of imatinib).