This textbook provides an overview of qualitative and quantitative methods used in different social sciences to investigate defence issues. Recently, defence issues have become of increasing interest to researchers in the social sciences, but they raise specific methodological questions. This volume intends to fill a gap in the literature on defence studies by addressing a number of topics not dealt with sufficiently before. The contributors offer a range of methodological reflections and tools from various social sciences (political science, sociology, geography, history, economics and public law) for researching defence issues. They also address the increasingly important question of data and digitalization. The book introduces the added value of quantitative and qualitative methods, and calls for a cross-fertilization of methods in order to facilitate better research on defence topics and to fully grasp the complexity of defence in the 21st century. This book will be of much interest to students, researchers and practitioners of defence studies, war studies, military studies, and social science research methods in general.