CHIR-99021 is a potent and selective inhibitor of GSK-3α and GSK-3β, commonly used in stem cell research to support the maintenance and self-renewal of pluripotent stem cells. It enables feeder-free culture of embryonic and induced pluripotent stem cells by activating the Wnt signaling pathway, which helps sustain pluripotency without differentiation. CHIR-99021 is also widely used in reprogramming somatic cells into induced pluripotent stem cells, improving efficiency when combined with other reprogramming factors. In regenerative medicine and disease modeling, it aids in directing stem cell differentiation into specific lineages such as cardiomyocytes and neural cells. Additionally, it is employed in organoid development and 3D cell culture systems to enhance cell survival and proliferation. Its role in modulating key signaling pathways makes it a valuable tool in developmental biology and drug discovery research.