Obviously you buy a book to read it, however they are non volatile and last centuries, so maybe you could flog them second hard or even give them to your kids!

As a rule of thumb the same book would be worth acsendingly more in this order - paperback, hardback, hardback (with dustcover), signed paperback, signed hardback. When you're buying second hand Celtic books these are the things to look for.

As well as this, take into account the edition of the book, first editions are likely to worth more.

The best things about books are that they provide entertainment as well as investments, as such you can pick them up everywhere.