Allelopathy refers to the effects of one plant on another plant through the release of chemical compounds into the environment. Chemicals released from plants. Imposing allelopathic influences (allelochamicals) are classified as secondary metabolites and are produced as offshoots of the primary metabolic pathways in plants. Allelopathic compounds play important roles in the determination of nutrient dynamics, mycorrhizae, soil chemical characteristics, microbial ecology, plant diversity, dominance, invasion, succession, and climax of natural vegetation. Species richness and diversity are important indicators of ecosystem function, which are influenced by allelopathic plants thereby affecting invasion and dominance of plants within natural ecosystems. Moreover, allelochamicals may affect plants species by inhibiting their microbial symbionts such as mycorrhizae and nitrogen-fixing bacteria. Allelopathic potential of most invasive species is expressed as one of the most important factors in their successful establishment in new habitats. Also, allelopathy makes a significant contribution to the process of plant succession. This chapter is based on a literature review on allelopathy from a perspectives of allelopathic plants, including plant biodiversity, microbial symbiosis, invasion, and plant succession.