Pierce Butler focused on the incubanula when he established the John M. Wing Foundation on the history of printing at the Newberry Library. The purpose of this paper is to interpret Butler's intention in building the incunabula collection by examining several aspects of his choices. Through examination of the classification in his incunabula catalogues and of his incunabula exhibition catalogues, two important characteristics of the incunabula collection are indicated as follows: (1) The process of the spread of printing in historical and geographical perspective. (2) The process of modern book-formation. Furthermore, it appears that Butler aimed to establish the incunabula collection as an expression of the diffusion of scholarship. It seems that Butler developed his thinking between book and culture during the Newberry's period.