Protein phosphorylation, the enzyme-catalyzed reversible addition of a phosphate group to protein residues, represents one of the most ubiquitous post-translational modifications (PTMs); it has been estimated that approximately 30% of all proteins are phosphorylated at some point in their lifetimes. Protein kinases catalyze the transfer of a phosphate group from molecules such as ATP to various amino acid residues, while phosphatases catalyze the reverse reaction. This reversible PTM can cause changes to the local and/or global structure of proteins, which may serve to modify their activity in key cellular pathways. protein, phosphorylation may alter its conformational ensemble and/or ability to bind to its biomolecular partners. Because phosphorylation represents a strong chemical perturbation to a protein, it is perhaps unsurprising that it is used by the cellular machinery to regulate important processes such as metabolism, apoptosis, membrane transport, cell signaling, and a variety of other essential cellular processes. Human genome mutations can result in improper function of the protein kinases and phosphatases that catalyze the addition and removal of phosphate groups from proteins, potentially leading to improper regulation of these key cellular pathways. This leads to diseases such as cancer, diabetes and various neurodegenerative disorders. Due to the central role that the kinases and phosphatases play in the regulation of these diseased pathways, phosphorylated systems are increasingly becoming promising targets for drug development strategies, demonstrating the importance of this PTM for proper cell function. Thus, the effects of protein phosphorylation must be studied thoroughly to understand how it modulates the regular functions of proteins and to understand how/why abnormal phosphorylation associated with disease disrupts these functions. The detailed study of these systems may significantly aid current drug development processes, in addition to furthering our basic understanding of cellular physiology.