Kiasma presents and collects the latest contemporary art. There are currently more than 8,000 works in the collection, with new acquisitions adding about 100 works every year. Kiasma mainly collects works by Finnish artists and artists living in nearby countries. It also adds to the collection by commissioning new work from artists.

Acquisitions by Kiasma are in the hands of an Acquisitions Committee, whose members include experts from Kiasma and two external artist members. Decisions are made by the Museum Director at the presentation of the Chief Curator of collections. The Acquisitions Committee keeps abreast of exhibitions and events in the art scene. Works are purchased from galleries as well as directly from artists themselves. The price is always set by the seller. Within its means, Kiasma also produces or co-produces works for its exhibitions, from which the works may end up in the museum's collections.

The collection is also added to by donations. The most important donated collections in Kiasma are the Porkkana Collection, the Kouri Collection collected by Pentti Kouri and donated to Kiasma by Postipankki, and works by Kalervo Palsa that were donated to the museum by Maj-Lis Pitkänen.