http://www.guggenheim.org/new-york/collections/collection-online/show-full/piece/?search=Paul Klee&page=1&f=People&cr=2

http://www.guggenheim.org/new-york/collections/collection-online/show-full/piece/?search=Paul Klee&page=1&f=People&cr=3

http://www.nortonsimon.org/collections/browse_artist.php?name=Klee,+Paul&resultnum=52

http://www.nortonsimon.org/collections/art.php?id=P.1953.025&type=fpx&title=The+Tree+of+Houses

http://www.guggenheim-venice.it/inglese/collections/artisti/dettagli/klee_ritratto_frau.html