The oak processionary moth is a serious forestry pest that is capable of causing complete defoliation of oak trees. Its caterpillars are also a hazard to health. Breeding populations of the moth were discovered for the first time in the UK in London in 2006 and these initial infestations have since spread and the moth has become more widely established. Controlling the moth is important, to protect trees from defoliation that can lead to decline and tree death, and to prevent risks to health. Control measures are most effective when applied at an early stage, before populations have started to increase. Effective control depends on monitoring the spread of the moth and detecting new outbreaks as soon as these arise, and also keeping track of abundance in areas where it is known to be present. There are a number of methods that can be used for monitoring but one of the most effective methods is to use pheromone traps. This Practice Note describes how these traps are used to capture oak processionary moths and what to do when moths are caught. It is aimed at forest and woodland managers, forestry practitioners, local authority tree and woodland officers, arboriculturalists and others who are actively involved with managing oak trees.