Deaccessioning is the formal process by which a museum, library, or archive permanently removes an object or item from its collection. It is the institutional equivalent of deciding to sell, transfer, or destroy a holding — and it is among the most contested decisions in collections management. What It Is Accession means to formally add something to a collection. Deaccession is the reverse: the institution decides that a particular item no longer serves its mission, is redundant, is too costly to preserve, or is better held elsewhere — and removes it from the permanent collection through a defined process.