This review explores the role of glycans in shaping the human gut microbiota, from birth to adulthood and across different dietary and environmental conditions. Glycans, including dietary plants, animal-derived cartilage, and endogenous host mucus, provide a diverse and dynamic environment for gut microorganisms to thrive. The review highlights how individual microorganisms degrade these glycans, the mechanisms of glycan acquisition, and the potential for manipulating this ecosystem for better health and nutrition. It discusses the impact of dietary glycans on microbial community composition, the role of endogenous glycans in maintaining stable nutrient sources, and the spatial distribution of glycans along the gastrointestinal tract. The review also examines microbial strategies for glycan acquisition, such as the Sus-like systems in Bacteroidetes and the ABC transporters in Firmicutes and Actinobacteria. Finally, it explores the formation of microbial food chains and the evolution of microbial genomes in response to selective pressures from glycans.This review explores the role of glycans in shaping the human gut microbiota, from birth to adulthood and across different dietary and environmental conditions. Glycans, including dietary plants, animal-derived cartilage, and endogenous host mucus, provide a diverse and dynamic environment for gut microorganisms to thrive. The review highlights how individual microorganisms degrade these glycans, the mechanisms of glycan acquisition, and the potential for manipulating this ecosystem for better health and nutrition. It discusses the impact of dietary glycans on microbial community composition, the role of endogenous glycans in maintaining stable nutrient sources, and the spatial distribution of glycans along the gastrointestinal tract. The review also examines microbial strategies for glycan acquisition, such as the Sus-like systems in Bacteroidetes and the ABC transporters in Firmicutes and Actinobacteria. Finally, it explores the formation of microbial food chains and the evolution of microbial genomes in response to selective pressures from glycans.