Patron-Driven Acquisition (PDA) is an e-book business model introduced by NetLibrary almost 10 years ago. The model was slow to develop over the years but has experienced a resurgence with programs from NetLibrary, Ingram Digital, and EBL. PDA stems from two traditional collection development principles—purchasing titles based on patron suggestions and establishing approval plans. The primary differences are that PDA is a business model strictly for e-books, and final selections are made by the patrons.