This document provides an introductionary lecture on endocrinology and the thyroid. It defines hormones and lists the major endocrine glands and their hormones, including the pituitary gland, thyroid gland, parathyroid gland, pancreas, adrenal glands, gonads, and hypothalamus. It then describes the mechanisms of action of hormones at cell membrane receptors, cytoplasmic receptors, and nuclear receptors. The document concludes with an overview of the thyroid, including its anatomy, histology, physiology, biochemistry, diagnosis, and surgical treatment.