The last decade has seen a dramatic increase inecological research on allelopathy, largely within thecontext of non-native species invasions. The vastmajority of these studies focus on determiningwhether a species is allelopathic and in determiningthe mode of action for the interaction. The case studyapproach is a useful first step, but it should notpreclude the integration of allelopathy into a broaderecological context. In preparing this special issue ofPlant Ecology on allelopathy, we have specificallyfocused on studies that place allelopathy into thecontext of environmental variation, species interac-tions, soil microbial communities, restoration, andother ecological processes. We have attempted to spanthe breadth of allelopathy research—incorporating abroad range of plant communities/ecosystems, geo-graphic locations, and taxonomic groups.We have adopted a broad view of allelopathy anditsconsequences. While theincorporation oftheGreekpathos (suffering) into the term suggests chemicalinteractions that are in some way inhibitory, we haveadopted the broader definition of ‘‘any chemicallymediated interactions among plants’’ (Rice 1974).That being said, most of the interactions describedhere are inhibitory. An interesting and related questionis, how much chemical mediation is necessary beforean interaction is considered to be allelopathic? Thealteration of local soil pH is a common impact of manyplant species that is not considered allelopathic, butwould certainly involve the release of chemicals fromplant tissues. Allelochemicals may have direct effectson other plants or they may be mediated through theaction of soil microbes. Ultimately, the effects ofallelopathic interactions may be expressed by changesin growth, competitive outcomes, and soil resourcedynamics, among others. Of course, any allelopathiceffects are only part of the potential suite of interac-tions between species, with the overall interactionreflecting the net effects of direct competition, facil-itation, and allelopathy. It is the overall direction andstrength of the interaction that will determine com-munity dynamics and structure.We havepulledtogethertwoverydifferentresearchareas andtheirapproachestoallelopathy inthisspecialissue. Allelopathic research within agricultural sys-tems has a long and largely continuous history,whereas interest in allelopathy in ecological systemshas ebbed and flowed over the years. By includingstudies of agro-ecosystems into this issue, we havetried to form connections between the two researchgroups. We pose that agricultural systems may beconsidered as useful model systems for understanding