The objective of this chapter is to introduce the endocrine system. Endocrine tissues are highly vascular. The secretions of endocrine glands are called hormones. Hormones travel through blood to the target cells whose functioning they may influence profoundly. A hormone acts on cells that bear specific receptors for it. The endocrine organs along with autonomic nervous system coordinate and control the metabolic activities and internal environment of the body. The endocrine glands are pituitary, pineal, thyroid, parathyroid, pancreas, suprarenal gland, testis or ovary. The pituitary gland (hypophysis cerebri) is a small endocrine gland, ovoid in shape, and is suspended from the base of the brain by a stalk. Thyroid gland is an endocrine gland, yellowish-brown in color, richly vascular. It maintains the metabolic rate, stimulates somatic and psychic growth and plays an important role in calcium metabolism. In this chapter, long essay type and short essay type questions are also provided.