New items enter the Foundation's collections in various ways. Besides federal and state government funding, assistance from private collectors, public and private charitable foundations, associations of friends, and other entities is essential. Unlike the museums, the libraries make a practice of routinely and systematically acquiring new items.

2014 von der Staatsbibliothek zu Berlin erworben: Die amerikanischen Reisetagebücher Alexander von Humboldts

Acquired in 2014 by the Staatsbibliothek zu Berlin: Alexander von Humboldt's American Travel Diaries © Staatsbibliothek zu Berlin

Right from the start, the museums took a wide-ranging and encyclopedic approach to collecting. Nowadays, the purpose of acquisitions is to fill gaps in the holdings – as, for example, with the purchase of Japanese lacquer vessels from the private collection of Klaus F. Naumann for the Museum für Asiatische Kunst, Staatliche Museen zu Berlin (Museum of Asian Art, National Museums in Berlin). Furthermore, purchases are sometimes made after a restitution, as in the case of two watercolors by Wilhelm Lehmbruck. These works had entered the possession of the Stiftung Preussischer Kulturbesitz as a consequence of Nazi persecution. After they had been restored to the rightful heirs, they were repurchased by the Foundation. 

Depending on the amount of money to be paid, final approval for an acquisition must be obtained from the Board, the President, or the director of the institution concerned. Objects and groups of objects can be purchased in different ways. Limited budgets have made it necessary to develop innovative solutions for enlarging the collections. One way of doing this is to make a purchase jointly with another institution. This was done in the case of the Kleiner Klebeband, an important collection of art drawings that was acquired jointly by the Kupferstichkabinett (Museum of Prints and Drawings) and the Augsburg Municipal Art Collections in 2011, with financial assistance from a large number of donors. 

Systematic acquisitions in libraries and archives

The libraries within the Foundation are continually and systematically acquiring books, periodicals, newspapers, estates, maps, electronic documents and other kinds of material that are relevant to their subject areas. Further material comes into the libraries' possession through the exchange of manuscripts.

The Staatsbibliothek zu Berlin (Berlin State Library) boasts over 25 million media, making it the largest academic universal library in the German-speaking countries. Every year their holdings are enlarged with countless new acquisitions such as books – increasingly e-books – as well as newspapers and periodicals in print and digital form. When deciding whether to purchase an object or collection, its usefulness in terms of both research and mediation work is taken into consideration. In 2016, a new electronic tool was introduced to help make the final decision on acquisitions. Known as "patron-driven acquisition" (PDA), this estimates the likely demand among library users for the item concerned. 

At the end of 2013, the Foundation landed a once-in-a-lifetime acquisition for the Staatsbibliothek zu Berlin: Alexander von Humboldt's American travel diaries. The purchase was made possible by huge support from private patrons and members of the public. The music collection has been enriched, for example, by the estate of singer, conductor, and writer Dietrich Fischer-Dieskau, which was given to the Staatsbibliothek zu Berlin. With its purchase of the Wagenbach Verlag archive (the part covering 1964–2004) in 2015, the Staatsbibliothek – with funding from the Cultural Foundation of the German States – continued its program of acquiring publisher's archives of literary and academic importance. 

The Ibero-Amerikanische Institut (Ibero-American Institute) is home to Europe's largest library specializing in Latin America, the Caribbean, Spain, and Portugal. It contains more than 1.7 million media (including approximately 930,000 printed books) and its holdings are growing steadily, thanks to many donations, among other things. 

The Kunstbibliothek der Staatlichen Museen zu Berlin (Art Library of the National Museums in Berlin) boasts around 400,000 volumes, making it a major library in the field of art history and theory. Its users also have access to some 1,400 international journals. A further 190,000 volumes are held by the Dienstbibliothek des Geheimen Staatsarchivs Preussischer Kulturbesitz (Service Library of the Prussian Secret State Archives). The library of the Staatliches Institut für Musikforschung (State Institute for Music Research) contains 67,000 volumes and subscribes to about 200 professional journals.

Acquisition with Grant Aid

Public grant-funding bodies such as the Cultural Foundation of the German States, the German Research Foundation, and the Federal Cultural Foundation also provide financial support for the SPK's acquisition projects. Generous support with acquisitions is also received from well-respected private cultural foundations. In addition, the holdings of the Foundation's various institutions are enriched at intervals by the bequest of estates. Bequests also offer a means of honoring and supporting the Foundation with monetary and non-monetary gifts. 

Many of the SPK's institutions also benefit from the dedication of the various associations of friends, which play a significant part in acquisitions. For example, the Friends of the Nationalgalerie regularly enable additions to the collection, ranging from paintings by Max Liebermann to the film installation Manifesto by contemporary artist Julian Rosefeldt. The Staatsbibliothek zu Berlin has likewise been assisted by its association of friends with the purchase of letters written by Thomas Mann.