British copyright law enjoins publishers to deposit one copy of every book they publish to six libraries: The British Library (formerly the British Museum), The National Libraries of Scotland and of Wales, and the University Libraries of Oxford, Cambridge, and Trinity College, Dublin. This obligation in one form or another dates back to the 17th century.

U.S. publishers only have to bother about the Library of Congress, though they need to send two copies if they register copyright. (Even if it’s not registered a book is still copyrighted. It’s just a bit harder to act against infringements if not the book isn’t registered, so most publishers do register their copyrights. This prosaic process is often left for someone’s spare time and has been known in some houses to fall a year or more behind schedule. The U.S. Copyright Office has a useful list of frequently asked questions.)

According to Wikipedia, Poland requires the deposit of 19 copies, so English-language authors and publishers shouldn’t feel too aggrieved.

See also Copyright registration.