This book is a companion volume to the Handbook on Electricity Markets, which focused on the evolution and challenges of wholesale electricity markets, particularly with the integration of intermittent renewable energy. This volume shifts the focus to the formally regulated segments of the electricity sector: network regulation, the functions of economic regulators, and the regulation of retail electricity. The content is structured into three distinct parts. The first part establishes the current state of electricity regulation, examining its foundations and recent reforms. The second part looks towards the future, exploring the regulatory implications of the path to net zero carbon emissions. The third part broadens the geographical scope to consider the unique regulatory landscapes of non-OECD countries. Parts I and II concentrate primarily on the United States (US), Great Britain (GB), Australia, and the European Union (EU). These jurisdictions have been selected because they are home to the oldest and most sophisticated frameworks for the economic regulation of electricity. Part III then turns its attention to the significant and evolving regulatory environments in India, China, and the broader category of lower[1]and middle-income countries (LMICs). The fundamental challenge of electricity regulation is to balance the control of monopoly prices with the promotion of efficiency, all while leveraging competition wherever it is viable. The rise of competitive wholesale and retail electricity markets has increasingly focused regulatory attention on transmission and distribution networks, which are typically separated from the more competitive parts of the sector. However, the extent of this separation varies; while Europe and Australia have established clear unbundling of networks, this remains an ongoing process in many other parts of the world. Looking ahead, this book examines how regulation must adapt to the changing characteristics of the power system as driven by net zero targets in the US and Europe. This includes exploring specific challenges such as developments 'behind the meter' (e.g., rooftop solar and batteries), fostering innovation within the regulated sector, and managing the profound uncertainty surrounding the future evolution of the energy industry. Two critical new areas of regulation necessitated by the net zero transition are also addressed: the regulation of green hydrogen markets and networks, and the regulation of electric vehicle (EV) charging infrastructure. Several overarching themes emerge from the comprehensive analysis presented by the contributing authors: First, the history of electricity regulation offers valuable lessons. It demonstrates that well-designed incentive regulation is a powerful tool for driving down costs while encouraging the quality of service and investment that society values. Second, the regulation of transmission is becoming increasingly complex. This is due to the practical difficulties of building new onshore infrastructure and the growing need for clear cost signals that guide the optimal location of both generation and demand to minimise system costs. Third, the regulation of distribution can be adapted to improve service quality and respond to user preferences for both generation and demand. However, it is crucial to design this regulation carefully to 10 avoid incentivising over-investment and to encourage the optimal substitution of operational expenditures for traditional capital investments where it is more efficient. Fourth, ambitious net zero targets are placing significant strain on existing incentive-based regulatory systems. These systems were often designed for mature networks where controlling costs was the primary objective. In the new era, mechanisms such as automatic adjustments, dedicated innovation funding, and more responsive regulatory approaches are becoming increasingly important. Fifth, achieving net zero may require fundamental changes to existing institutional arrangements. Many current structures of network ownership, system operation, and regulation were established before the net zero era and may need to be reformed to align with decarbonisation goals. Finally, many developing countries continue to face the foundational challenge of establishing effective, independent regulation. This basic level of governance is essential to attract the massive private and public investment needed to deliver electricity at reasonable costs, with acceptable service quality, and with minimal environmental impact. While the principles of good regulation are universal, their application in developing countries requires navigating unique political and economic contexts. This digest aims to provide decision-makers with a comprehensive overview of the key principles, challenges, and future directions in electricity regulation, drawing from the rich insights and detailed analysis contained within the full Handbook.