Biography.com: Eucken, Rudolf Christoph: A one-paragraph biography.
Eucken, Rudolf Christoph: Biographical entry from the 2001 Columbia Encyclopedia.
Rudolf Christoph Eucken: Wikipedia article on this German ethical thinker.
Rudolf Eucken: Biography and bibliography, from the Books and Writers project.
The Nobel Prize in Literature 1908: Awarded to Eucken. Biography and full text of his Nobel lecture are available.