The parathyroid glands are small endocrine organs, which are located near the thyroid gland. The parathyroid glands play a central role in calcium balance through the secretion of parathyroid hormone (PTH). Parathyroid disease includes a range of disorders that disturb calcium balance, resulting in several biochemical abnormalities and clinical manifestations. Surgery has a key role in many parathyroid diseases including benign, malignant, and hormonal disease processes. This chapter provides an in-depth exploration of the types, pathophysiology, clinical features, diagnosis, and treatment of parathyroid diseases.