Bundling has also been used to segment the used book market. Each combination of a textbook and supplemental items receives a separate ISBN. A single textbook could therefore have dozens of ISBNs that denote different combinations of supplements packaged with that particular book. When a bookstore attempts to track down used copies of textbooks, they will search for the ISBN the course instructor orders, which will locate only a subset of the copies of the textbook.

Legislation at state and federal levels seeks to limit the practice