Endocrinology is a branch of medicine that is concerned with the study of the endocrine system, its associated diseases and hormonal secretions such as insulin, thyroid hormone and growth hormone. Hormones are classified into the classes of amines, steroids, and peptides and proteins. A number of endocrine feedback mechanisms are integral to the working of the endocrine system. These act in such a way that one feedback mechanism controls the release or action of another hormone. Some endocrine diseases are hypothyroidism, diabetes mellitus and metabolic syndrome, among others. Most of such disorders require lifelong care. The diagnosis of endocrine disorders is performed by laboratory techniques especially through inhibition/suppression testing or excitation/stimulation testing. Different approaches, evaluations, methodologies and advanced studies on endocrinology have been included in this book. There has been rapid progress in the understanding of endocrine disorders, their diagnostic techniques and treatments, which have been included in this extensive book. It is an essential guide for both academicians and those who wish to pursue this discipline further.