The article discusses the critical role of adult intestinal stem cells in maintaining epithelial homeostasis and regeneration. Small populations of adult stem cells, residing in specialized niches, are responsible for the continuous renewal and repair of the intestinal epithelium throughout life. Recent advancements in identifying specific markers for these stem cells and developing new technologies to track their activity in vivo have significantly enhanced our understanding of stem cell-driven processes in the intestine. These insights have potential implications for developing stem cell-based therapies and improving cancer treatments. The inner epithelial lining of the small intestine is a multifunctional tissue that must efficiently digest and absorb nutrients while maintaining a barrier against harmful microorganisms and carcinogens. This high rate of cell turnover necessitates the presence of adult stem cells, which reside in specialized niches and can self-renew and generate new functional epithelia. The discovery of robust markers for these stem cells and the development of ex vivo culture systems have enabled researchers to better understand how stem cells interact with their niche to maintain homeostasis and how they contribute to intestinal cancer. The article also highlights the identification of 'reserve' stem cells that can be rapidly recruited to maintain epithelial homeostasis following injury, suggesting that epithelial cells separate from the regular stem cell pool also have regenerative potential. Additionally, a nutrient-sensing mechanism within the stem cell niche that regulates the size and activity of the stem cell pool has been identified, which could be exploited for therapeutic applications. The review discusses the current models of stem cell-driven epithelial homeostasis and repair in the intestine, including the 'stem cell zone model' and the '+4 model', and the emerging unifying theory that incorporates aspects of both models. It also covers the identification and validation of specific markers for intestinal stem cells, such as Lgr5, Sox9, Msi1, Prom1, BMI1, HOPX, LRG1, and TERT, and the regulatory mechanisms that control their activity and fate.The article discusses the critical role of adult intestinal stem cells in maintaining epithelial homeostasis and regeneration. Small populations of adult stem cells, residing in specialized niches, are responsible for the continuous renewal and repair of the intestinal epithelium throughout life. Recent advancements in identifying specific markers for these stem cells and developing new technologies to track their activity in vivo have significantly enhanced our understanding of stem cell-driven processes in the intestine. These insights have potential implications for developing stem cell-based therapies and improving cancer treatments. The inner epithelial lining of the small intestine is a multifunctional tissue that must efficiently digest and absorb nutrients while maintaining a barrier against harmful microorganisms and carcinogens. This high rate of cell turnover necessitates the presence of adult stem cells, which reside in specialized niches and can self-renew and generate new functional epithelia. The discovery of robust markers for these stem cells and the development of ex vivo culture systems have enabled researchers to better understand how stem cells interact with their niche to maintain homeostasis and how they contribute to intestinal cancer. The article also highlights the identification of 'reserve' stem cells that can be rapidly recruited to maintain epithelial homeostasis following injury, suggesting that epithelial cells separate from the regular stem cell pool also have regenerative potential. Additionally, a nutrient-sensing mechanism within the stem cell niche that regulates the size and activity of the stem cell pool has been identified, which could be exploited for therapeutic applications. The review discusses the current models of stem cell-driven epithelial homeostasis and repair in the intestine, including the 'stem cell zone model' and the '+4 model', and the emerging unifying theory that incorporates aspects of both models. It also covers the identification and validation of specific markers for intestinal stem cells, such as Lgr5, Sox9, Msi1, Prom1, BMI1, HOPX, LRG1, and TERT, and the regulatory mechanisms that control their activity and fate.