Galectin-3 is a 26kDa B-galactoside-binding protein belonging to the Galectin family, which consists of more than ten members. Galectin-3 is composed of a carboxyl-terminal carbohydrate recognition domain (CRD) and amino-terminal tandem repeats. Galectin-3 normally distributes in epithelia of many organs and various inflammatory cells, including macrophages as well as dendritic cells and Kupfer cells. The expression of this lectin is up-regulated during inflammation, cell proliferation and cell differentiation and through transactivation by viral proteins. Its expression is also affected by neoplastic transformation: upregulation is found in certain types of lymphomas, and thyroid carcinoma, while it is down regulated in other types of malignancies such as colon, breast, ovarian and uterine carcinomas. The expression of Galectin-3 has a strong correlation with the grade and malignant potential of primary brain tumors. Increased Galectin-3 levels have also been noted in human atherosclerotic lesions. These findings suggest that Galectin-3 expression is affected during these physiological and pathological responses. Galectin-3 has been shown to function through both intracellular and extracellular actions. It is a component of heterogeneous nuclear ribonuclear protein (hnRNP), a factor in pre-mRNA splicing and has been found to control cell cycle and prevent T-cell apoptosis through interaction with the Bcl-2 family members. On the other hand, this protein, which is secreted from monocytes/macrophages and epithelial cells has been demonstrated to function as an extracellular molecule in activating various types of cells such as monocytes/macrophages, mast cells, neutrophils and lymphocytes. Galectin-3 has been shown to mediate cell-cell and cell-extracellular matrix interactions and acts as a novel chemoattractant for monocytes and macrophages.