Thyroid cancer is increasing all over the world. The exact cause of this increase is still debated and there are conflicting reports. Sophisticated molecular studies suggest that environmental chemicals may have effects of thyroid carcinogenesis. The development of powerful molecular biology techniques has enabled targeted next-generation sequencing for detection of mutations in thyroid cancer, and this technique can make a specific diagnosis of thyroid cancer in cytologically indeterminate cases. The initial treatment of well-differentiated thyroid cancer (DTC) is surgery followed by radioiodine remnant ablation. However, further studies are needed to determine the optimal dosage of radioactive iodine for DTC patients with lateral neck metastasis. DTC is an indolent tumor and may cause death even decades later. Thus, long-term follow-up is mandatory. Recently, dynamic risk stratification (DRS) has begun to use stimulated thyroglobulin level at 1 year after the initial treatment and restratified the risk in accordance with the response to the initial treatment. This DRS strategy accurately predicts disease free survival and can be widely used in daily clinical settings. For the iodine refractory metastatic disease, redifferentiation therapy and targeted therapy are two promising alternative treatments. Sorafenib is the first approved agent for the treatment of progressive iodine refractory advanced thyroid cancer in Korea and may be very helpful for radioactive-refractory locally advanced or metastatic DTC. Selumetinib may be an effective redifferentiating agent and could be used within several years.