This chapter presents a state of the art summary of parathyroid tumors relation to its biology, epidemiology, disease mechanisms, clinical signs, diagnosis, treatment and prognosis. Tumors affecting the parathyroid glands include parathyroid adenoma, diffuse hypercellularity, and parathyroid carcinoma. Parathyroid carcinoma is a rare malignant endocrine cancer, representing 0.55% of parathyroid tumors and 0.4%–5.2% of primary hyperparathyroidism. Parathyroid tumors have a prevalence of 0.1%–0.4% in the general population and up to 4% in postmenopausal women, and they mainly affect adults. Clinicopathologically, parathyroid tumors are defined by vascular invasion, perineural invasion, gross invasion into adjacent anatomical structures, and metastasis. Treatment of choice for parathyroid tumors is surgery, along with preoperative medical management to lower elevated calcium levels and to correct other metabolic disturbances due to hyperparathyroidism. Hypercalcemia-related symptoms in functional tumors may be controlled by cinacalcet HCl, bone antiresorptive agents, and calcimimetic agents.