This chapter discusses the targeting subunits for protein phosphatases. Protein phosphatase 1 (PP1), one of the major protein-serine/threonine phosphatase catalytic subunits in eukaryotic cells, does not exist as a monomer in vivo, but as complexes with other proteins that target it to particular subcellular locations, modify its substrate specificity, and appear to be the key to its regulation. The role of these phosphorylations is unknown. In view of the multiple phosphorylation sites and role of A-kinase and ISPK phosphorylation, this important region of the G subunit is termed “phosphoregulatory domain.” This chapter discusses the structure, localization, and regulation of glycogen-associated enzyme—PPlG. The observed effects of PP1G activity of ionic strength, pH, G-C subunit interaction, and binding of glycogen to PPIG and substrates emphasize the importance of using near-physiological conditions for assessment of phosphatase function.