This book presents the frontier research of toxicology and health risk assessment of chemicals. First, it provides an overview of the current methods of evaluating safety amounts of chemicals and provides a new aspect of the principle of toxicology. Secondly, it shows recent research where the new method of health risk evaluation is adopted, followed by an integrated health risk assessment of chemicals. Finally, it describes the epigenetic inheritance of chemical impact on health throughout several generations. Estimating the safety amount of chemicals surrounding our lives is not sufficient for health risk evaluation, particularly for carcinogenic compounds, endocrine disruptors, and nano materials. The author’s group has found a family of chemicals linked to ADHD through animal screening and identified its chemical nature using chemoinformatics methods. Based on these new developments, this book proposes to utilize the biomarker common to those chemicals for health risk assessment, independent of exposure routes and physiological dimensions. The book appeals to researchers and students in the field of toxicology, health risk assessment, pharmacology, and public health.