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 spontaneous differentiation. It is widely used in regenerative medicine and cellular reprogramming protocols. CHIR-99021 also plays a role in directed differentiation, particularly in protocols aiming to generate cardiomyocytes and neural progenitor cells. Its ability to modulate key signaling pathways makes it a valuable tool in developmental biology and drug discovery research involving stem cell models.