Bookbinding is the process of compiling a book from a number of mere papers. There are various techniques in use today.
Books bought today tend to be of one of these four categories:
A hardbound book has hard covers and is stitched in the spine. Looking from the top of the spine, you can see that the book consists of a number of signatures bound together. If you open the book in the middle of a signature and look, there should be a thread.
A paperback book consists of a number of loose pages glued together in the spine. Quite often, they fall apart after some use.
A cardboard article looks like a hardbound book at first sight, but it is really a paperback with hard covers. It is not as durable as a real hardbound; often the binding will fall apart after a little use.
A sewn book is constructed in the same way as a hardbound book, except that it lacks the hard covers. The binding is as durable as a hardbound book.
When talking about book binding as a craft, it is almost exclusively hardbound books that are done. When rebinding a sewn book, one usually turns it into a hardbound book by adding hard covers.
Books can be bound in lots of different materials. Some of the more common materials for covers are leather and cloth (see also: buckram). A common way to bind a book is as a halfbound book, which means that the spine and the corners of the cover are covered with leather or cloth, while the rest is covered with paper (normally marbled or otherwise decorated).