The thyroid gland, taking its name from ‘thyreos’, is a shield-shaped gland located in front and below the larynx. The gland is made up of follicles filled up with colloid. These follicles synthesise thyroid hormones—tri-iodothyronine and tetra-iodothyronine, which control key metabolic functions in the human body. In addition, they also control neural and cardiovascular functions and play strong roles in neurodevelopment as well. Thyroid gland pathologies present commonly to the clinics and are important from a burden of disease perspective. In the present chapter, we provide an overview of the gland, structure–function relationship, key actions of its hormones and common pathologies presenting to the clinics.