The central idea in building and maintaining an item bank is to calibrate all the items onto a "common variable." The arithmetic involved in the calibration process is presented. It is recommended that an analysis of fit be done in every application to verify that the estimates of item difficulties are in fact sample-free. These procedures are explained. Once an item bank is built, a common calibration for all items should be established and routinely checked. Special procedures for adding new items, updating old items, and dropping obsolete items are described. (BW)