The natural and artificial chemicals in our environment interact in intricate ways. We've been making use of and living in close proximity to these materials for quite some time. It is crucial to comprehend how chemicals affect both people and the environment. This book delves into the field of toxicology, investigating the interactions between toxic substances and human health. In this comprehensive work, we journey through the intricate world of toxicology, beginning with an introduction to the significance of chemicals in our lives and the regulatory frameworks governing their use. We explore how toxicology, the study of the adverse effects of chemicals on living organisms, plays a pivotal role in ensuring our safety. The terminology used in toxicology, along with the fundamental concepts of somatic, germline, and stem cells, and the vital concept of homeostasis, are elucidated in detail. As we progress, we delve into the mechanisms by which chemicals can harm people, distinguishing between chronic and acute exposures. The book also sheds light on the various classes of toxicants, from air pollutants and soil contaminants to workplace toxicants and chemicals used in agriculture. It outlines the diverse range of toxic substances, from metals like lead and mercury to pesticides, herbicides, and toxins from insects, algae, and mycotoxins. Toxicokinetics, the study of how the body interacts with toxic substances, is a central theme. We explore the processes of absorption, distribution, metabolism, and excretion (ADME) and the different pathways by which chemicals enter our bodies. The role of the liver in metabolizing toxic compounds is examined in detail. The dynamics of toxicology are unveiled, including the effects of metabolites on cell damage, covalent binding, calcium control loss, and the generation of free radicals. Cutting-edge approaches like omic-age mechanistic toxicology, which encompasses the transcriptome, proteome, and metabolome, are also discussed. The book then shifts its focus to the environmental effects of toxicology, highlighting the impact of toxic substances on vital organs such as the liver, kidney, immune, respiratory, and nervous systems. The adverse consequences of chemicals that disrupt hormones are explored, along with their effects on both human health and the environment. A significant portion of this work is dedicated to toxicity risk assessment and human health protection. It covers various aspects, including hazard identification, dose-response analysis, exposure assessment, and the prevention of toxicity. The book also addresses regulatory aspects and the importance of domestic toxin abatement, emphasizing the need for effective prevention measures in workplaces and the environment. Finally, this book aims to raise awareness and educate readers about the critical importance of safeguarding against environmental pollution. It underlines the significance of effective education in empowering individuals and communities to make informed choices and contribute to a healthier, safer world. This comprehensive guide to toxicology serves as a valuable resource for students, researchers, policymakers, and anyone seeking a deeper understanding of the intricate world of chemicals and their impact on human health and the environment. It is our hope that this book will not only inform but also inspire individuals to take active steps toward a safer and more sustainable future Any unintended errors, mistakes, omissions, and improvements of this book are most welcome.