Oak trees are angiosperms, meaning their seeds are protected (by acorns in oaks) and distributed by animals. Most oaks lose their leaves in the fall, but there are evergreen oaks as well. Oaks are typically slow-growing, long-lived trees with hard wood.

Oaks are dominant in temperate, deciduous forests where summers are warm and winters are cold (such as most of Europe, western Asia and eastern North America). Plant and animal diversity is higher than in boreal forests, but lower than in tropical forests.

Oaks were sacred to Zeus, particularly at the sanctuary at Dodonoa where an oak tree served as an oracle whose rustlings were interpreted by the priestesses. Nature spirits, such as the Hamadryads, were associated with specific trees, which they would defend from intruders. 