Improvement in the outcome of cancer patients who are refractory to currently available treatments relies on the development of target-directed therapies. One group of molecular targets with potential clinical relevance is a set of protein tyrosine kinases encoded mostly by proto-oncogenes and that are frequently deregulated in cancer. Glycogen synthase kinase 3β (GSK3β), a serine/threonine protein kinase, has emerged as a therapeutic target for common chronic diseases including type 2 diabetes mellitus, neurodegenerative disorders, inflammation and osteoporosis. This is based on its currently known functions and primary pathologic causalities. GSK3β has well characterized roles in the regulation of gene transcription and in oncogenic signaling. We have shown that deregulated GSK3β promotes gastrointestinal, pancreatic and liver cancers and glioblastomas. Furthermore, we have demonstrated that inhibition of GSK3β attenuates cancer cells survival and proliferation, induces cell senescence and apoptosis and sensitizes tumor cells to chemotherapeutic agents and ionizing radiation. This has led us to propose GSK3β as a potential therapeutic target in cancer. The anti-tumor effects of GSK3β inhibition are mediated by changes in the expression and phosphorylation of molecules critical to the regulation of cell cycling, proliferation and apoptosis and underlie the pathological role for GSK3β in cancer. Investigation of the mechanisms responsible for deregulation of GSK3β and the consequent downstream pathologic effects in cancer cells has shed light on the molecular pathways leading to tumorigenesis. This will allow exploration of novel therapeutic strategies for cancer that target aberrant GSK3β.