Within intellectual history there has been a widening interest over the last decades in rediscovering intellectuals who used to be renowned when they were active, but who for various reasons have been more or less forgotten over time. The Swedish writer Ellen Key (1849–1926) was a famous intellectual who gained her reputation through books, pamphlets, and hundreds of lectures on topics such as pedagogy, peace, and women’s rights—topics that were at the top of a general intellectual agenda around 1900. I will focus on her idea of internationalism that was founded on an evolutionary life philosophy of development. Her engagement in internationalism was built on an idealist foundation of philosophical, religious, and humanitarian beliefs organized around peace and a problematization of the nation. Key advocated a kind of patriotism as her path towards developing internationalism. In this article, Key’s work is contextualized and conceptualized in the discussion of internationalism of her contemporaries.