Anaplastic thyroid carcinoma (ATC) is a rare but highly aggressive endocrine malignancy characterized by rapid progression, poor prognosis, and limited therapeutic options. Despite advances in thyroid cancer management, ATC continues to pose significant clinical challenges, with a median survival of only a few months. This chapter reviews key controversies in the diagnosis and management of ATC, emphasizing molecular pathogenesis, clinical presentation, and evolving treatment paradigms. Multimodality therapy—including surgery, radiotherapy, and systemic therapy—offers the best outcomes in carefully selected patients, while targeted therapies and immunotherapy have redefined management for subsets with actionable mutations. Novel strategies such as neoadjuvant targeted therapy, adjuvant immunotherapy, and experimental approaches (cell therapy, virotherapy, and combination regimens) are being actively investigated. Early palliative care integration and multidisciplinary coordination remain essential. Ongoing clinical trials provide cautious optimism that ATC outcomes may improve through precision oncology.