Unfortunately, the Library cannot afford to purchase textbooks and still maintain the subscriptions and other resources needed by students and faculty for research. Also, one copy of a textbook would not be sufficient for an entire class. Sometimes a professor will place a personal copy of the textbook on reserve, but not every professor has access to extra copies.
If your professor has announced that a required textbook is on reserve in the library, search "Course Reserves" by the course number or the professor's name.
Occasionally, you'll find a required textbook in the Library Catalog, located at the UH Anderson Library or UHD library. If the book is not on reserve or checked out, use the catalog's Request feature to have it transferred to UHCL's Circulation Desk or to the UHCL Pearland Library.
You can search for textbooks on the bookstore's website by course number.
