Following a brief discussion of the diagnosis and classification of hypoparathyroidism, this review will focus on current concepts of pseudohypoparathyroidism. Topics to be covered will include differing resistance of kidney and bone to parathyroid hormone, relationship of estrogen and pregnancy to Ca homeostasis, normocalcemic pseudohypoparathyroidism, and current understanding of pathogenesis based on various defects in the hormone receptor-adenylate cyclase system. Evidence for physiologic derangements beyond the impaired generation of cyclic AMP will be reviewed, as well as involvement of nonendocrine systems by the deficiency of the stimulatory guanine nucleotide connecting protein. Finally, semantic confusion resulting from the faulty term “pseudopseudohypoparathyroidism” will be addressed.