Quercus - Associação Nacional de Conservação da Natureza (Quercus - National Association for Nature Conservation) is a Portuguese environmental organization founded in 1985. The name Quercus is used because the Oak (Quercus in Latin) is one of the species that is characteristic in this country and that nowadays is increasingly rare. Its headquarters are in the Monsanto Forest Park, in Lisbon.

On their website, Quercus declares itself to be a non-profit national environment organization, independent from political parties.