The Image Archive of the main library at the Swiss Federal Institute of Technology in Zurich (ETH-Bibliothek) is home to a vast collection of photographs. It includes material collected by professors and other staff at the ETH, images created and collected by institutes and chairs within the ETH, but also the entire archives of companies or other institutions, such as Switzerland's legendary former national airline Swissair (1931 - 2001), or private collections bequeathed to ETH-Bibliothek. The aim of the new book series 'Pictorial Worlds. Photographs from the ETH-Bibliothek's Image Archive' is to build a bridge between analytical treatment of historical image sources and the interest in individual photographs for any possible reason. One of the collections held at the Image Archive has been put together by Swiss entrepreneur Adolf Feller (1879 - 1931) and his daughter Elisabeth (1910 - 1973). Unique in size, scope and period covered, it comprises 54,000 postcards from 1889 - 1980. It documents comprehensively what can be called the Golden Age of picture postcards before World War I, with its enormous diversity of motifs, radical changes of style in design and when postcards had their heyday as a communication medium. The collection's main focus is on images of individual sites, places and landscapes in 140 countries. Around 15,000 motifs are from Switzerland. The period best represented in the collection is from 1893 - 1930. The World in Pocket-size Format is a documentation of this magnificent collection. The book is also an illustrated history of this means of communication that has had its time of utmost importance in human relationships.