This book investigates the role of gas networks in future low-carbon energy systems, and discusses various decarbonisation pathways, providing insights for gas network operators, developers, and policy makers. As more countries around the world move towards low-carbon energy systems and increase their exploitation of renewable energy sources, the use of natural gas and the associated infrastructure is expected to undergo a substantial transformation. As such there is a great uncertainty regarding the future role of gas networks and how they will be operated in coming years. The topics addressed include: Fundamentals of gas network operation The impact of variable renewable electricity generation on the operation and expansion of gas networks The impact of decarbonising heat supplies on gas networks Opportunities and challenges of utilising gas networks to transport alternative low-carbon gases such as bio-methane and hydrogen