Thyroid eye disease is a cell-mediated autoimmune disorder associated with systemic Graves Disease. It is the most common orbital disease causing proptosis in adults. The primary target of the immune response is the thyroid stimulating hormone (TSH) receptor site on the orbital fibrocyte. A cytokine-mediated reaction results in inflammation, glycosaminoglycan deposition, tissue edema, and adipogenesis. Patients usually present with proptosis, eyelid edema, chemosis, and eyelid retraction. Motility restriction is common from extraocular muscle enlargement and fibrosis, and dicreased vision can result from optic nerve compression. Imaging shows enlargement of extraocular muscles and increased orbital fat. An active inflammatory phase is usually followed by a chronic non-inflammatory phase. Treatment in the inflammatory phase involves orbital radiotherapy, systemic or intraorbital steroid injection, and most recently with a clinical course of teprotumumab injections. Surgery for reduction of proptosis (orbital decompression) and eyelid retraction can be offered in the chronic phase.