Anaplastic carcinoma thyroid, also known as undifferentiated thyroid carcinoma, is a rare but highly aggressive malignant tumor, which accounts for 2–3% of all thyroid malignancies. It is mostly seen in elderly females in their 6th or 7th decade. It carries a very bad prognosis with an average median survival of 5 months. Patients often present with a rapidly growing, painful, woody hard lower anterior neck mass fixed to underlying structures. In addition to local invasion, patients also present with regional nodal spread and distant metastasis. Though the risk factors for anaplastic carcinoma thyroid are unknown, most of them develop in the setting of long-standing goiter, possibly in an undiagnosed, well-differentiated thyroid carcinoma. Management of anaplastic carcinoma thyroid demands a multidisciplinary approach with the involvement of surgeon, radiation oncologist, radiologist, and endocrinologist. The conventional treatment of anaplastic carcinoma thyroid includes surgery, radiation, and chemotherapy. Recently, multitarget tyrosine kinase inhibitors are also incorporated into the treatment. However, prognosis of the disease is very poor with 4 months of overall survival of 35% and overall disease-specific mortality of 98–99%. In this chapter, we discuss how to approach the condition and various treatment strategies to provide improved treatment outcomes for patients diagnosed with anaplastic carcinoma thyroid.