Book excerpt: This book provides information on best practices and new thinking regarding the validation of alternative methods for toxicity testing. It covers the validation of experimental and computational methods and integrated approaches to testing and assessment. Validation strategies are discussed for methods employing the latest technologies such as tissue-on-a-chip systems, stem cells and transcriptomics, and for methods derived from pathway-based concepts in toxicology. Validation of Alternative Methods for Toxicity Testing is divided into two sections, in the first, practical insights are given on the state-of-the-art and on approaches that have resulted in successfully validated and accepted alternative methods. The second section focuses on the evolution of validation principles and practice that are necessary to ensure fit-for-purpose validation that has the greatest impact on international regulatory acceptance of alternative methods. In this context validation needs to keep pace with the considerable scientific advancements being made in toxicology, the availability of sophisticated tools and techniques that can be applied in a variety of ways, and the increasing societal and regulatory demands for better safety assessment. This book will be a useful resource for scientists in the field of toxicology, both from industry and academia, developing new test methods, strategies or techniques, as well as Governmental and regulatory authorities interested in understanding the principles and practicalities of validation of alternative methods for toxicity testing.