By 1914, Belgium and the Netherlands had maintained a foreign policy of neutrality for nearly a century. For these two similarly sized, neighbouring countries in northwest Europe, it was not an occasional stance, but a long-term position that persisted in times of peace. Belgium had been neutralised at the time of its independence; the Netherlands had opted for it voluntarily. This thesis investigates how neutrality was constructed and employed by Belgium and the Netherlands and how the policy was debated in official circles as well as the public sphere, focusing on the period from 1899 to the start of the First World War. It aims to connect the concept of neutrality, hardly ever considered outside the realm of diplomatic history, to processes of nationalism and national identity formation. For Belgium and the Netherlands, neutrality was more than a security policy. Being neutral, vowing not to take part in conflict, also impacted heavily on how the Belgians and the Dutch perceived themselves in Europe and the world at large. Neutrality was never universally supported in either country. During these years, opponents viewed it as humiliating to their nation and they frequently advocated for abandoning it. Merging neutrality with nationalism through its construction as a mission to foster peace in Europe was essential when it came to strengthening the policy’s domestic popularity. It fulfilled a widespread desire for a national purpose and for a sense of agency in international affairs. This forms a crucial part of the explanation for the policy’s longevity. Both the Belgians and the Dutch thus turned their neutrality from a position of weakness into one of strength.