Toxicology, the scientific study of the adverse effects of chemical substances on living organisms, encompasses various branches including general, mechanistic, regulatory, and descriptive toxicology. Regulatory guidelines for conducting toxicity studies are established by organizations such as the OECD, ICH, EPA, and India's Schedule Y, ensuring standardized protocols and safety measures. The principles of Good Laboratory Practice (GLP) are fundamental in drug development, guaranteeing quality and integrity in laboratory studies. The history and evolution of toxicology highlight its crucial role in advancing drug development and ensuring the safety of pharmaceuticals and chemicals.