The chemokine receptor CXCR4 belongs to the large superfamily of G protein-coupled receptors and has been identified to play a crucial role in a number of biological processes, including the trafficking and homeostasis of immune cells such as T lymphocytes. CXCR4 has also been found to be a prognostic marker in various types of cancer, including leukemia and breast cancer, and recent evidence has highlighted the role of CXCR4 in prostate cancer. Furthermore, CXCR4 expression is upregulated in cancer metastasis, leading to enhanced signaling. These observations suggest that CXCR4 is important for the progression of cancer. The CXCR4-CXCL12 (stromal cell-derived factor 1 (SDF-1)) axis has additionally been identified to have a role in normal stem cell homing. Interestingly, cancer stem cells also express CXCR4, indicating that the CXCR4-SDF-1 axis may direct the trafficking and metastasis of these cells to organs that express high levels of SDF-1, such as the lymph nodes, lungs, liver, and bone. This review focuses on the current knowledge of CXCR4 regulation and how deregulation of this protein may contribute to the progression of cancer.