Endophytes (fungal and bacterial organisms) have attracted great interest over the past few years because their presence benefits the host plant (development and defence) and they are a source of secondary metabolites of potential interest and thus play an important role in the regulation of plant communities and their herbivores. There are an increasing number of reports on their identification and on the production of secondary metabolites. Their role in plant-pathogen and plant-insect interactions is receiving increasing attention because of their potential use in pest control, however, little is known about their physiology and the regulation processes of the plant-endophyte interaction.