This open access book is a coherent and accessible source of knowledge on flexibility services for energy. Local flexibility services are a commercial mechanism which allows participants to be renumerated for delivering a change in their usual power use, in real time or in response to prior request from the Distribution System Operators (DSOs) to help manage network congestion. Summarising key outputs from the Energy Networks Association's (ENA) Open Networks Programme, the book traces the evolution of local flexibility markets from 'Proof of Concept' to 'Business as Usual'. The book presents detailed technical and organisational insights from the development of local flexibility markets, focusing on inception, standardization, simplification, and transparency in decision-making across GB DSOs and interactions with the National Energy System Operator (NESO). Readers will find valuable comparisons of implementation approaches by different network companies, highlighting technical nuances and best practices. Ideal for researchers, energy professionals, and policymakers, this book provides a critical resource for understanding the complexities and opportunities of flexibility services in energy systems. Whether you are involved in energy management, policy development, or academic research, this book offers essential insights into the future of energy flexibility and grid management.