Conserving genetic resources in trees. What is being done, and what role do arboreta play? Tor Myking and Kjersti Bakkebø Fjellstad discuss the role of arboreta in conserving tree ‘genetic resources’, defined as within species diversity in traits that are relevant for human use. This is compared to the neutral term, ‘genetic diversity’, reflecting within-species genomic variation. Both are pertinent in the context of human mediated climate change. Achievements in ‘in situ’ conservation of tree genetic resources (i.e., within natural populations) through European projects such as EUFORGEN are described. Arboreta instead present potential for ‘ex situ’ conservation. Examples are drawn from the Arboretum: Sorbus species and European holly (Ilex aquifolium).