The strategy of applying kinase inhibitors as effective therapeutic agents has achieved unparalleled success in the past decade, while it is still a daunting challenge to develop kinase inhibitors with desirable selectivity among different kinase families. This chapter describes the basic conceptions in the field of kinase selectivity, available profiling technologies, and quantification of selectivity levels. The chapter highlights the different selectivity of approved kinase inhibitors, which include non-covalent type I and II ATP-competitive inhibitors, allosteric inhibitors, one lipid kinase inhibitor, and covalent inhibitors. Most approved kinase inhibitors are multitarget or unselective inhibitors that bind with the highly conserved ATP pocket, high selectivity is more likely to be achieved among kinases with only few closely related homologs or unique structural features in binding sites.