This theme covers collections which are groups of unique objects that form the core of a museum or gallery’s activities such as exhibitions, education and research.  Normally only objects in certain categories and of a certain quality are accepted into the collection.

Because museums cannot collect everything, each potential new addition must be carefully considered as to its appropriateness for a given museum's defined area of interest.  The process by which an object is formally included in the collection is called accessioning.

Museum collections are widely varied such as collections of art, of scientific specimens, of historic objects and of living zoological specimens.  Most museums have a specific area of specialization. For example, a history museum may only collect objects relevant to a particular county or even a single person, or focus on a type of object such as industry or stamps. Art museums may focus on a period, such as modern art, or a region.

The process of managing a collection – accessioning, caring, exhibiting, storing, lending and borrowing objects – is known by the collective name of Collections Management.