Book excerpt: Positive Psychology Across the Life Span provides an insight into how we are affected by the different stages of adult development and gives us the opportunity to change through choice rather than leaving change to chance. The science of positive psychology offers a wealth of research and evidence-based interventions and shares insights into which habits and behaviours contribute to how to live a flourishing life. This book aims to extend that knowledge by introducing and incorporating key aspects of existential and humanistic psychology and explores positive psychology with a lifespan perspective. It goes beyond theory to look at practical application, with insightful reflective questions. Whilst acknowledging the differences and disagreements between some of the key figures in the subject areas of the book, it seeks to highlight the areas where there is agreement and congruence which have been previously overlooked or ignored. The book will be essential reading for students and practitioners of positive psychology as well as other mental health professionals.