The concept of willingness to defend plays a significant role in contemporary Finnish discussions on defence. A high level of willingness to defend among the Finnish population is considered crucial for the foundation of Finland's defence policy. This book is based on the premise that a country may need to emphasize opinion or attitude-based factors to support its national defence capability and it explores the idea of will or willingness in the context of organizing defence. But what does the idea of will or willingness mean in the first place when talking about organizing defence, and what kind of resource the idea of will or willingness might be in defence policy? This peer-reviewed monograph utilizes scholarly literature as well as published and archival sources to explore Finnish history from the 1920s until 2022 and to theoretically and empirically understand the phenomenon. To carry out this exploration, the book analyzes political language featuring connections between resources and notions of the idea of will or willingness. As a result, a comprehensive and conceptual long-term view of Finnish defence policy thinking emerges, showing how important the idea of will or willingness has been in Finland.