Hormone is substance produced by specialized cells in specific glands and transported in circulation to distance where it acts on target tissues. Peptides, steroids, catecholamines, etc. are some types of hormones. Growth hormone-releasing hormone (GHRH) stimulates anterior pituitary to secrete growth hormone. Sermorelin is GHRH analogue used to diagnose growth hormone (GH) deficiency. Somatostatin is present in hypothalamus, parts of central nervous system (CNS), pancreas and gastrointestinal tract (GIT). It inhibits secretion of GH, thyroid stimulating hormone (TSH), prolactin (PRL), insulin, glucagon and intestinal secretions. Thyrotropin-releasing hormone, corticotropin-releasing factor, gonadotropin-releasing hormone, etc. are other hypothalamic hormones which are mentioned in this chapter. A detailed discussion on anterior pituitary hormones has been also presented in this chapter.