Thyroid gland enlargement (goiter) is a common problem in clinical practice. Goiter may be diffuse or nodular, either multinodular goiter (MNG) or a single nodule, and may be toxic or nontoxic. Symptoms of MNG can range from none to life-threatening compressive symptoms. Iodine deficiency is the most common cause of goiter worldwide. Diagnostic evaluation should address functional status and anatomical and morphological characteristics, and the risk of cancer in MNG is similar to single nodules. Based on the functional status and morphology, treatment options vary from observation to radioiodine or surgery. Nonsurgical, minimally invasive approaches are also available with certain limitations. In this chapter, we describe toxic and nontoxic MNG, epidemiology, pathogenesis, diagnostic, and therapeutic options.