A broad range of disorders can cause inflammation of the thyroid gland. True thyroid infections are rare and can result from a variety of microorganisms, of which bacteria are the most common. Other rarer pathogens include fungi, parasites, and viruses. Gram-positive bacteria, especially staphylococci, predominate as causative agents in adults and children. In immunocompromised patients, opportunistic pathogens have been isolated. Most infections in adults occur as a result of hematogenous or lymphatic seeding of the thyroid gland. In children, congenital anomalies can lead to thyroid infection and require surgical correction to prevent recurrence. Fine-needle aspiration of the thyroid is usually required to identify the infecting agent, and prolonged antimicrobial therapy with or without surgical drainage is the cornerstone of management. This review outlines the pathogenesis, microbiology, diagnosis, and management of infectious thyroiditis in adults and children and compares this disorder with other, more common causes of thyroid inflammation.