Glycogen synthase kinase-3 (GSK-3) is a multifunctional serine/threonine kinase found in all eukaryotes. It is a key regulator of numerous signaling pathways, including those involving Wnt, receptor tyrosine kinases, and G protein-coupled receptors. GSK-3 is involved in various cellular processes, such as glycogen metabolism, cell cycle regulation, and proliferation. Unlike most protein kinases, GSK-3 is usually constitutively active and regulated through inhibition of its activity. It has a preference for primed substrates, which are phosphorylated by another kinase. This review discusses the regulation of GSK-3 in various pathways, including its role in the Wnt/β-catenin pathway, the Hedgehog pathway, and its regulation by serine and tyrosine phosphorylation. Recent advances in understanding GSK-3 regulation, including the crystal structure of GSK-3 and its interaction with substrates, are highlighted. The review also addresses the development of GSK-3 inhibitors and their implications for therapeutic applications. GSK-3 is involved in multiple diseases, including diabetes, Alzheimer's disease, and cancer. Its role in these diseases is linked to its regulation of key signaling pathways. The review emphasizes the importance of understanding GSK-3's regulation to develop effective therapeutic strategies.Glycogen synthase kinase-3 (GSK-3) is a multifunctional serine/threonine kinase found in all eukaryotes. It is a key regulator of numerous signaling pathways, including those involving Wnt, receptor tyrosine kinases, and G protein-coupled receptors. GSK-3 is involved in various cellular processes, such as glycogen metabolism, cell cycle regulation, and proliferation. Unlike most protein kinases, GSK-3 is usually constitutively active and regulated through inhibition of its activity. It has a preference for primed substrates, which are phosphorylated by another kinase. This review discusses the regulation of GSK-3 in various pathways, including its role in the Wnt/β-catenin pathway, the Hedgehog pathway, and its regulation by serine and tyrosine phosphorylation. Recent advances in understanding GSK-3 regulation, including the crystal structure of GSK-3 and its interaction with substrates, are highlighted. The review also addresses the development of GSK-3 inhibitors and their implications for therapeutic applications. GSK-3 is involved in multiple diseases, including diabetes, Alzheimer's disease, and cancer. Its role in these diseases is linked to its regulation of key signaling pathways. The review emphasizes the importance of understanding GSK-3's regulation to develop effective therapeutic strategies.