Google has attempted to answer the question of how many books exist in a very interesting blog post. http://booksearch.blogspot.com/2010/08/books-of-world-stand-up-and-be-count… Why am I posting this to Foundation-l? Well, one of the things it reveals is the difficulty of answering this question and I hope that it has some relation to Wikimedia projects; in particular, I didn't know that multiple books (entirely unrelated books) have shared ISBNs. So, if nothing else, it might impact... http://en.wikipedia.org/wiki/Wikipedia:ISBN And I also thought that Google's attempt to catologue all books was parallel to our goal of... well, I'm not sure that we ever say we're attempting to catalogue ALL knowledge... but we seem to be making a decent fist of it so far. Nevertheless, I confess that I'm still not sure I should be posting this to Foundation-l... and it strikes me that perhaps the only guidance I can find on what should be posted could perhaps be fleshed out a little more: https://lists.wikimedia.org/mailman/listinfo/foundation-l Apologies if this email strikes you as cruft. Still, damn interesting blog post, eh?