Oak trees in Britain have long suffered from dieback and decline disorders, but a disease called acute oak decline has been causing particular concern since the first few years of the 21st century. A typical symptom of the disease is dark, sticky fluid bleeding from small cracks in the bark on the trunk of the tree. This stem bleeding can be extensive, with as many as 20 or more bleeding patches on an infected tree, and the canopy can become thin as the tree approaches death. Some trees die within four or five years of the onset of symptoms. Our research has revealed that three previously undescribed bacteria are involved. The condition appears to be most prevalent in warmer parts of England and Wales that are prone to drought and atmospheric nitrogen pollution. Woodland managers should survey, record and monitor infected trees and take the appropriate recommended action, which might include felling diseased oaks. Felled material should not be removed from affected sites unless the bark and sapwood have been removed and destroyed. This publication provides more-detailed advice and guidance on managing the disease.