Some of this depends on your definition of “book”. The oldest printed book is in Burns Library. It is Jean Gerson’s De Spiritualib[us] Nupciis (On Spiritual Marriage) from about 1470. Lots more info about it, and a link to the digital version, here: bit.ly/ReallyOldBook. We also have a manuscript (handwritten book) from ~1300: http://burnsantiphoner.bc.edu. That is essentially an old church song book. I’m not sure about smallest. Do you mean height/width or thickness? Or smallest total volume? Either way, I might not be able to find a good answer.