Plants, whither wild or cultivated, interact with each other and other organisms (micro- and macro-organisms) in several ways. These interactions are based on the chemical release from plants and are studied as “allelopathy” under the domain of ecology. The interactions often result in a resource-driven dominance of certain plant species over others. Under natural ecosystems, such interactions are generally regarded as the causative factors for modifying the distribution of flora while in managed agro-ecosystems, the interactive capabilities of plants can be exploited for bringing potential improvements in the production of crops in a sustainable way. Since managed agriculture mainly relies on appropriate agricultural practices and input of diverse synthetic chemicals for attaining high yields of crops, concurrently they have also resulted in considerable ecological and environmental problems. To address the issues of sustainability in agriculture, natural approaches are strongly encouraged. Allelopathy may provide an effective mechanism to control weeds and pest and may contribute to soil fertility. This would lead to reduced application of fertilizers and pesticides, thus ensuring durable agriculture. In this chapter we present a brief review about allelopathy, underlying mechanisms and its roles in natural and managed ecosystems.