Thyroid cancer is the most common endocrine cancer. Researchers are intensely studying the molecular pathogenesis of differentiated thyroid carcinoma. Novel agents such as multikinase inhibitors have been introduced in the treatment of advanced differentiated thyroid carcinoma and have revolutionized the treatment of this disease. The molecular pathogenesis of poorly differentiated and anaplastic thyroid carcinoma is under research and may introduce novel agents in the treatment of this extremely rare but lethal disease. These novel and exciting advances are the subject of the book at hand.