Existentialism is a catch-all term for those philosophers who consider the nature of the human condition as a key philosophical problem and who share the view that this problem is best addressed through ontology. This very broad definition will be clarified by discussing seven key themes that existentialist thinkers address. Those philosophers considered existentialists are mostly from the continent of Europe, and date from the 19th and 20th centuries. Outside philosophy, the existentialist movement is probably the most well-known philosophical movement, and at least two of its members are among the most famous philosophical personalities and widely read philosophical authors. It has certainly had considerable influence outside philosophy, for example on psychological theory and on the arts. Within philosophy, though, it is safe to say that this loose movement considered as a whole has not had a great impact, although individuals or ideas counted within it remain important.