A document that is printed on both sides of the page and bound into a book-like form (even a document that is duplex-printed on an office printer and placed in a folder) will form two-page spreads with a left-hand and a right-hand page. Also, because a book is bound, it is easier to see the details near the outer edges of each page as you leaf through the document than it is to see the inner edges of the page near the binding. Thirdly, the sequential reading order of the pages makes it convenient to think of each two-sided leaf of the document as having a ‘front’ and a ‘back’ side.

All of these aspects can affect the page design. For example, chapter openings are typically (but not exclusively) on the right-hand of a spread, since that is the ‘front’ side of a leaf. Page numbers and any other navigation aids on a page are more likely to be on or near the outer edge of each page so they can be seen more easily when leafing through the document. Thinking of the document as a sequence of two-page spreads also raises questions of whether the facing pages should be symmetrical around the gutter and whether items such as graphics can span across the two pages.