Patron-driven acquisition (PDA), also referred to as demand-driven acquisition (DDA),[1] is a model of library collection development in which a library only purchases materials when it is clear that a patron wants them.
In an ideal transaction, libraries provide the patron with access to search engines, academic databases and/or library catalogs from which the patron can request items.
[4] There are several benefits to focusing this practice on the use of digital content: delivery is instantaneous; e-books require no physical space, which requires specific costs to maintain; libraries can afford patron access when they might not be able to afford to buy materials, increasing the collection's ability; and purchases are guaranteed usage, which is an important consideration when purchasing materials.
[3] Libraries typically index ebooks that are available for purchase in their catalogs or discovery layers.
The University of Iowa reported that this type of system, when unmediated by library collection development staff, can lead to a very high level of purchases.