Natural enemies regulate the populations of many insects, including non-native insect pests. Accidental introduction is one of the ways through which natural enemies of non-native insect pests accumulate in the invaded range. In plantation forestry, numerous species of natural enemies have been reported to be accidentally introduced around the world. Several of these natural enemies were initially introduced as biological control agents and subsequently spread, without intentional intervention, to other countries. Other accidentally introduced natural enemies were likely introduced through pathways such as live plant trade and wood materials with their pests. Some of these natural enemies have provided good control of the populations of their host insects after accidental introduction. This demonstrates how such introductions may contribute to pest management, without the financial investment and time required to implement a classical biological control programme. However, potential negative effects of these accidental introductions, such as non-target effects, also need to be considered. These case studies highlight the need for regular surveillance to keep information current about the diversity and distribution of natural enemies and their impact on pest populations in a region.