Ellen Key (1849–1926) was one of Europe's most influential thinkers on issues of motherhood and women's sexuality during the early 1900s. This anthology maps how her ideas were reformulated in Europe's five major language areas – English, German, French, Italian, and Spanish – and explores how her ideas about social modernity and women's sexuality were received and how they were communicated in feminist literature and debate during the first decades of the 20th century. The aim of this anthology is to offer new knowledge about Key's influence on European thinking on issues such as motherhood, sexuality, and love in the early 1900s by offering both a broader and deeper understanding of the international significance of Key's work.