An ex-library book once belonged to a public, school or subscription library and was later withdrawn and sold. Libraries mark and protect their books heavily, so ex-library copies carry signs of that use that collectors treat as significant faults.
How to spot it
Look for a library stamp on the title page, the edges of the text block or a plate; a pocket, date label or card holder inside a cover; a spine label with a shelf number; and "Withdrawn" or "Discarded" stamps. Many library jackets were glued or taped into a plastic cover, and some books were rebound in hard-wearing library buckram. Removed labels and pockets usually leave marks, so look for scuffed or discoloured patches.
What it does to value
Ex-library copies sell for a fraction of the price of a clean copy, often a small fraction for a modern first edition, because the marks cannot be fully removed. For a scarce book where clean copies hardly exist, an ex-library copy may still be the only realistic way to own one and keeps a real, if lower, value. A few books were sold mainly to libraries, so collectors accept library copies more readily for those titles.
Our ex-library books guide shows the common marks and what each does to value.