# What is the EPUB spine?

Source: https://epublab.com/glossary/spine/ (updated 2026-11-03)

The spine is the ordered list, inside the OPF package document, of the content documents a reader pages through from start to end. It sets the default reading order of the book.

## Why it matters when you convert a PDF to EPUB

When EPUBLab turns a PDF into an EPUB, chapters detected from the PDF's outline or heading sizes become separate documents, and their order in the spine is the order you read them. The spine must contain at least one linear item, and each manifest item may appear in it only once.

Items marked linear="no" are skipped when paging through, so they must be reachable from a link. The spine also carries page-progression-direction for right-to-left books.