Allelochemicals are substances involved in a natural phenomenon called allelopathy, where these substances are released by an organism into its living environment, affecting surrounding organisms. Among allelochemicals, phenolics represent the largest group, characterized by a basic structure of a benzene ring (C6) connected to a hydroxyl group (-OH). Decades of extensive research on phenolic allelochemicals have demonstrated their significant contribution to mediating diverse ecological interactions in a sustainable and environment-friendly manner. In this chapter, current knowledge of the effects of phenolic allelochemicals and their action mechanisms is highlighted. Additionally, we present their classification, distribution, release, and degradation. The isolation and identification methods for phenolic allelochemicals are also demonstrated. Based on that, we come up with discussions and perspectives on the advantages and existing challenges. Accordingly, promising approaches are proposed including: (i) to develop eco-friendly herbicides with high effectiveness; (ii) to establish highly efficient intercropping systems; (iii) to generate allelopathic crops accumulating dominant contents of phenolic allelochemicals through the regulation of affecting factors and the application of genetic engineering techniques; and (iv) to apply smart farming for optimizing the use of phenolic allelochemicals, monitoring their levels, and promoting sustainable agriculture. In essence, the information assembled in this chapter may provide valuable insights for future strategies, focusing on the development of green agriculture and management of ecological balance in accordance with sustainable development targets.