The phosphorylation state of a biologically relevant molecule affects its activity, reactivity, and ability to interact with other molecules. The enzymes responsible for adding phosphate groups, kinases, act on many types of molecules including proteins, lipids, carbohydrates, and nucleotides. These kinases mediate multiple signal transduction pathways and are responsible for modulating many essential cellular functions including metabolism, proliferation, differentiation, and survival. Dysfunction of kinases is involved in many pathological states including cancer, neurodegeneration, inflammation, metabolic and developmental disorders, and autoimmune diseases.