Allelopathy is an important ecological phenomenon influencing ecosystem dynamics. Currently, it has gained attention due to the potential applications of allelochemicals in agriculture. Allelopathic interactions have been reported in ecological relationships between plants and microorganisms, and between species of each group. These studies have been relatively descriptive, however, without interconnected views of how these molecules can affect cell biology and how they are integrated into environmental interactions. The present review provides an overview of the history, physiology, and ecological effects of allelopathy, with special focus on its occurrence between macro-and microorganisms and its ecological roles in terrestrial and aquatic environments. We have attempted to examine the interconnections between terrestrial and aquatic systems in relation to the production, dynamics, and ecological effects of allelochemicals and to discuss the possible effects of climate changes on allelopathic interactions.