Pseudohypoparathyroidism (PHP) is a rare endocrine disease caused by pathogenic GNAS gene variants. The clinical manifestations are a combination of PTH resistance (hypocalcemia, hyperphosphatemia, and elevated serum intact PTH), multihormone resistance, and/or Albright’s hereditary osteodystrophy (AHO). This chapter provides an overview of PHP subtypes, clinical features (Fig. 1), molecular basis and clinical implications and management with specific focus on obesity. For individuals with a suspected diagnosis of PHP, molecular testing should include sequencing, copy number variants (CNV) and methylation analysis of the GNAS locus.