The use of barcodes has varied over the years. The following is a list of those most commonly found:
- Aleph system-generated barcode. Numeric, with a varying number of digits (currently no more than 7 digits, but bound to get longer over time)
- Staff-supplied barcode. 14 digit numbers beginning "32044" (designating Harvard). As of 3/2008, used for material both on-site and at the Harvard Depository.
Obsolete Harvard Depository barcode. 6 characters long, both alphabetic and numeric. Begins with a two letter location code (locally HH for Houghton and HT for Theatre).