Plant pathogens are ubiquitous and recent research has provided us with dramatic examples of plant pathogens strongly influencing plant fitness, population dynamics, plant-herbivore interactions, community structure, invasion dynamics, and ecosystem function. However, we still know relatively little about the ubiquity and impact of plant pathogens in non-agricultural systems. The goal of this session is to bring together ecologists who work on a variety of plant pathogen systems at a variety of levels of biological organization. Recent research has shown that infection alters plant volatile emissions and induced plant defenses, thereby influencing both second and third trophic levels. Plant pathogens can drive invasions; for example, barley yellow dwarf virus has facilitated the invasion of California grasslands by exotic annual grasses. Endemic pathogens can help maintain high levels of biodiversity, while invasive pathogens like sudden oak death can completely transform native ecosystems. The speaker order will follow the order of biological scale, starting with individual-level processes and ending with ecosystem-level processes. Speakers will address a diverse range of plant pathogen systems including viruses, fungi, and bacteria in both temperate and tropical ecosystems.