Kinases are important drug targets that control cell growth, proliferation, differentiation and metabolism. This process involves phosphorylation of multiple substrates in cellular signal transduction pathways. Here, the authors provide a synopsis on assay technologies, mechanistic considerations for assay design and development pertaining to kinase enzymes. This chapter, along with some of the earlier chapters in this manual on basics of enzyme assays, mechanism of action and purity and identity considerations, serves as an excellent resource for beginners in HTS applications.