Throughout the twentieth century, office buildings became central to the organisation of societies – yet what went on inside them has remained remarkably understudied. Behind Office Doors explores this history by focusing on users and everyday practices. It examines how office spaces were conceived by architects, designers and managers, and how they were inhabited, experienced and contested by workers. From filing cabinets and air conditioning to EU offices and colonial bureaucracies, the chapters trace how design, technology and organisational thinking shaped office life. Alongside case studies on Europe, North America, Asia and colonial Africa, the contributions reflect on how the office has been approached in historiography. Drawing on cross-disciplinary research, this book argues for the development of historical office studies, showing how the design and management of offices have shaped cultures of work.