From A List Apart. The simple elgance and ergonomics of CSS is something I find fascinating:

A printed book has many features not seen on screens. There are page numbers, headers and footers, a table of contents, and an index. The content must be split into pages of fixed size, and cross-references within the book (for example, “see definition on page 35”) must be resolved. Finally, the content must be converted to PDF, which is sent to the printer.

Web browsers are good at dealing with pixels on a screen, but not very good at printing. To print a full book we turned to Prince, a dedicated batch processor which converts XML to PDF by way of CSS. Prince supports the print-specific features of CSS2, as well as functionality proposed for CSS3.