In the United States, the Commonwealth, Scandinavia and for books in Dutch, titles are usually written top-to-bottom on the spine. This means that when the book is placed on a table with the front cover upwards, the title is oriented left-to-right on the spine. This practice is reflected in the industry standards ANSI/NISO Z39.41 and ISO 6357.

In most of continental Europe and Latin America, titles are conventionally printed bottom-to-top on the spine so, when the books are placed vertically on shelves, the title can be read by tilting the head to the left. This allows the reader to read spines of books shelved in alphabetical order in accordance to the usual way left-to-right and top-to-bottom.

Wikipedia: Bookbinding, Orientation