Inside Google Books: “We collect metadata from many providers (more than 150 and counting) that include libraries, WorldCat, national union catalogs and commercial providers. At the moment we have close to a billion unique raw records. We then further analyze these records to reduce the level of duplication within each provider, bringing us down to close to 600 million records. Does this mean that there are 600 million unique books in the world? Hardly. There is still a lot of duplication within a single provider (e.g. libraries holding multiple distinct copies of a book) and among providers — for example, we have 96 records from 46 providers for “Programming Perl, 3rd Edition”. Twice every week we group all those records into “tome” clusters, taking into account nearly all attributes of each record…Is that a final number of books in the world? Not quite. We still have to exclude non-books such as microforms (8 million), audio recordings (4.5 million), videos (2 million), maps (another 2 million)…and other items for which we receive catalog entries… Counting only things that are printed and bound, we arrive at about 146 million. This is our best answer today. It will change as we get more data and become more adept at interpreting what we already have…After we exclude serials, we can finally count all the books in the world. There are 129,864,880 of them. At least until Sunday.”