Quercus may refer to:

• Oak, a term that can be used as part of the common name of any of about 400 species of trees and shrubs in the genus Quercus (from Latin "oak tree").
• Quercus (organization), a Portuguese association for the conservation of the natural environment.
• Quercus (software), an open-source pure Java implementation of the PHP scripting language, utilising a PHP/Java Bridge
• Quercus (publisher), a British publishing house

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