Plantations of eucalypts (species of Eucalyptus and Corymbia), particularly in the tropics and Southern Hemisphere, have expanded dramatically during the course of the last 100 years. The nature of these plantations has changed substantially as selection, breeding, hybridisation, vegetative propagation and other innovative techniques have been introduced to improve planting stock. Although there are various examples of diseases and pests damaging early plantations, it is clear that separation of the trees from their natural enemies has resulted in exceptional performance. Not surprisingly, both the incidence and impact of diseases and pests in eucalypt plantations has increased over time. This has been due to the accidental introduction of pests and pathogens from areas where the trees are native to new environments. There are also growing examples of host-specific pathogens native to areas where eucalypts have been planted as non-natives, which have undergone sometimes surprising host jumps. These 'new pathogens' threaten not only plantation forestry based on non-natives, but also eucalypts and their relatives in areas where they grow naturally. There is little question that pests and pathogens are set to challenge eucalypt plantation forestry worldwide, more than ever before. In order to sustain profitable businesses based on eucalypt plantations, forestry companies will need to invest substantially in technologies enabling management of these pests and diseases.