The article explores the mechanisms underlying the coexistence of diverse microbial species and the role of functional redundancy in microbial systems. It highlights that many coexisting microorganisms can encode the same metabolic functions, which contrasts with the expectation that species should occupy distinct metabolic niches. The authors argue that both functional redundancy and taxonomic variability are not primarily driven by ecological drift but are emergent properties of open microbial systems, influenced by biotic interactions and environmental and spatial processes. They discuss the implications of these findings for understanding microbial community assembly and function, emphasizing the importance of considering functional traits rather than just taxonomic composition in microbial ecology. The article also reviews recent studies that demonstrate the decoupling of functional composition from taxonomic composition in various microbial communities, suggesting that functional redundancy is a common feature of microbial systems. Finally, it explores mechanisms promoting functional redundancy, such as niche differentiation along multiple axes and the role of predation and antibiotic warfare, and concludes that functional redundancy is an inevitable outcome of open microbial systems, shaped by a high-dimensional trait space.The article explores the mechanisms underlying the coexistence of diverse microbial species and the role of functional redundancy in microbial systems. It highlights that many coexisting microorganisms can encode the same metabolic functions, which contrasts with the expectation that species should occupy distinct metabolic niches. The authors argue that both functional redundancy and taxonomic variability are not primarily driven by ecological drift but are emergent properties of open microbial systems, influenced by biotic interactions and environmental and spatial processes. They discuss the implications of these findings for understanding microbial community assembly and function, emphasizing the importance of considering functional traits rather than just taxonomic composition in microbial ecology. The article also reviews recent studies that demonstrate the decoupling of functional composition from taxonomic composition in various microbial communities, suggesting that functional redundancy is a common feature of microbial systems. Finally, it explores mechanisms promoting functional redundancy, such as niche differentiation along multiple axes and the role of predation and antibiotic warfare, and concludes that functional redundancy is an inevitable outcome of open microbial systems, shaped by a high-dimensional trait space.