One can almost think of "The Gutenberg Galaxy" as the "prequel" to Marshall McLuhan's much better known "Understanding Media," because "Galaxy" does for print techology what "Media" does for electronic technology. Basically McLuhan assesses how European civilization went from an ear-touch (listening) oriented mode of receving information to an eye-oriented (that is, reading) mode of receiving information. Recalling that for McLuhan, the medium IS the message, so the invention and dissemination of printing-press technology and the sharp rise in literacy it occasioned therefore brought about a major seismic shift in Western thought and all that goes with it--language, mores, dress, politics, etc.
Another way of looking at this is to say that in McLuhan's view, history is not determined by politics or economics or weather or science per se so much as by our media--the "extensions of man." This book is a must-read followup to anyone who liked "Understanding Media"; it's also a great book to cut one's teeth on before reading "Understanding Media" because it's a more traditional (i.e., formal and linear) type of academic work. And undeniably brilliant. For what it's worth, I was a communications major at the University of Virginia in the mid-1970s when reading McLuhan's work was rougher than it is now; many of his concepts like "global village" have since filtered thru society. But I read all of McLuhan's media-oriented writings, wrote term papers on him, and feel as though I benefited as a result--he's the main reason I'm a writer today.