Molecular biology emerged from advances in biochemistry during the 1940s and 1950s, when the structure of the nucleic acids and proteins were elucidated. Beginning in the 1970s, with nucleic acid enzymology and the discovery of the restriction enzymes, the tools of molecular biology became widely available and applied in cell biology to study how genes are regulated. This new knowledge impacted endocrinology and reproductive biology since it was largely known that the secretion of the internal glands affected the phenotypes, and expression of genes. Modern reproductive biology encompasses every level of biological study from genomics to ecology, encompassing cell biology, biochemistry, endocrinology and general physiology. All of these disciplines require a basic knowledge, both as a tool and as an essential aid to a fundamental understanding of the principles of life in health and disease. Overall, molecular biology is central to scientific studies in all living matter, impacting disciplines such as medicine, related health sciences, veterinary, agriculture and environmental sciences. In this book, the basic biochemistry of nucleic acids and proteins are reviewed. Methodologies used to study signaling and gene regulation in the endocrine/reproductive system are also discussed. Topics include mechanisms of hormone action and several endocrine disorders affecting the reproductive system. Professionals in the medical, veterinary and animal sciences fields will find exciting and stimulating material enhancing the breadth and quality of their research.