Protein kinases are now recognised as an important class of drug targets. Whilst many protein kinase inhibitors directly interact with the ATP-binding site, Gleevec is a notable example from a new class of allosteric inhibitors that alter protein kinase conformation to block productive ATP binding. Recently, kinase inhibitors with different mechanisms of action have also been described. Some of these are allosteric inhibitors that alter kinase conformation and prevent protein substrate binding. Other inhibitors directly compete with protein substrate binding. These inhibitors promise exciting therapeutic opportunities by exploiting new mechanisms of action and may thus allow greater specificity in protein kinase inhibition with fewer off-target side effects.