Adult stem cells are essential for tissue renewal and regeneration. Previous models suggested a single quiescent stem cell population in a tissue niche, but recent evidence shows coexistence of quiescent and active stem cell subpopulations in separate yet adjacent locations. These subpopulations have distinct but cooperative roles. Stem cells can self-renew and differentiate into multiple cell types. In invertebrates, germ stem cells (GSCs) reside in a niche and divide asymmetrically. In mammals, adult stem cells are generally quiescent. However, some long-lived cycling stem cells have been identified. The hair follicle provides a model system where quiescent and active stem cells coexist. Bulge stem cells are quiescent, while hair germ cells are active. Label-retaining cells (LRCs) in the bulge are identified as stem cells. Some LRCs remain quiescent, while others cycle. Lgr5+ cells in the bulge and hair germ are active and proliferate during anagen. In the gut, quiescent stem cells are located at the +4 position, while active stem cells are Lgr5+ cells in crypts. These cells give rise to transit amplifying (TA) cells. In bone marrow, quiescent hematopoietic stem cells (HSCs) are located in the endosteal region, while active HSCs are in the central marrow region. These HSCs have different cycling behaviors. The zoned model suggests that quiescent and active stem cells coexist in separate zones with distinct microenvironments. Quiescent stem cells can replace damaged active stem cells, and vice versa. This system ensures tissue regeneration and repair. The microenvironmental signals, such as Wnt and BMP, regulate stem cell states. The zoned model provides a better explanation for stem cell function and tissue renewal.Adult stem cells are essential for tissue renewal and regeneration. Previous models suggested a single quiescent stem cell population in a tissue niche, but recent evidence shows coexistence of quiescent and active stem cell subpopulations in separate yet adjacent locations. These subpopulations have distinct but cooperative roles. Stem cells can self-renew and differentiate into multiple cell types. In invertebrates, germ stem cells (GSCs) reside in a niche and divide asymmetrically. In mammals, adult stem cells are generally quiescent. However, some long-lived cycling stem cells have been identified. The hair follicle provides a model system where quiescent and active stem cells coexist. Bulge stem cells are quiescent, while hair germ cells are active. Label-retaining cells (LRCs) in the bulge are identified as stem cells. Some LRCs remain quiescent, while others cycle. Lgr5+ cells in the bulge and hair germ are active and proliferate during anagen. In the gut, quiescent stem cells are located at the +4 position, while active stem cells are Lgr5+ cells in crypts. These cells give rise to transit amplifying (TA) cells. In bone marrow, quiescent hematopoietic stem cells (HSCs) are located in the endosteal region, while active HSCs are in the central marrow region. These HSCs have different cycling behaviors. The zoned model suggests that quiescent and active stem cells coexist in separate zones with distinct microenvironments. Quiescent stem cells can replace damaged active stem cells, and vice versa. This system ensures tissue regeneration and repair. The microenvironmental signals, such as Wnt and BMP, regulate stem cell states. The zoned model provides a better explanation for stem cell function and tissue renewal.