The symphony has long stood as one of music's most prestigious and enduring forms, yet in Britain and Ireland its story since 1900 remains surprisingly underexplored. This landmark volume offers the first comprehensive account of the symphony's trajectory across the twentieth and twenty-first centuries, revealing a rich, multifaceted tradition shaped by an extraordinary diversity of voices, styles, and contexts. Drawing together distinguished international scholars and composers, the book surveys both celebrated figures such as Elgar, Vaughan Williams, and Tippett, and lesser-known yet vital contributors including Ruth Gipps, Ina Boyle, and Alan Bush. Through historical, analytical, and critical perspectives, contributors examine commissioning networks, cultural influences, performance traditions, and questions of identity, representation, and reception. Contemporary reflections by leading composers extend the discussion into the present, where changing approaches and aesthetics challenge and expand definitions of the symphony itself. Accessible, authoritative, and groundbreaking, this volume redefines our understanding of the British and Irish symphony - past, present, and future.