Thyrotoxicosis is a clinical syndrome of hypermetabolism and hyperactivity that results from excessive quantities of the thyroid hormones. It ranges in severity from subclinical hyperthyroidism to life threatening thyroid storm. The most common cause of thyrotoxicosis is Graves’ disease, followed by toxic multinodular goiter (TMNG), solitary toxic adenoma and thyroiditis. Graves’ disease, toxic multinodular goiter, toxic adenoma, thyroiditis are associated with thyrotoxicosis. It may also cause other laboratory abnormalities such as hyperglycemia, hypercalcemia, elevated alkaline phosphatase, leukocytosis, and elevated liver enzymes. Thyroid nuclear imaging studies and anatomic studies like thyroid ultrasound are different imaging modalities may assist in the determination of the etiology of this disease. Radioactive iodine uptake, scanning and thyroid sonography are very useful tools in the diagnostic evaluation methods. The thionamides and beta-adrenergic blocking drugs are used as treatment and are useful adjuncts to the management of thyrotoxicosis. Apart from these, this chapter also discusses about different management strategies.