Galectin-3 is a member of the lectin family, which includes 15 mammalian lectin members. Like all galectins, galectin-3 contains a carbohydrate recognition binding domain of about 130 amino acids that enables the specific binding of β-galactosides. This protein has been shown to be involved in cell adhesion, cell activation, chemoattraction, cell growth and differentiation, cell cycle, and apoptosis. Galectin-3 induces pro-inflammatory cytokines and inhibits Th2 type cytokine production. It chemoattracts monocytes and macrophages, and activates and degranulates basophils and mast cells. It was reported that galectin-3 knock-out mice demonstrated reduced phagocytic properties in macrophages and Kupffer cells, indicating that this protein is involved in macrophage phagocytosis. Galectin-3 has been shown to be involved in cancer, inflammation, fibrosis, heart disease, and stroke. It has also been shown that the expression of galectin-3 is implicated in a variety of processes associated with heart failure, including myofibroblast proliferation, tissue repair, inflammation, fibrogenesis, and ventricular remodeling. In addition, galectin-3 was found to contribute to tumor cell evasion of the immune system. Galectin-3 is increasingly being used as a diagnostic marker for different cancers. It can be screened for and used as a prognostic factor to predict the progression of the cancer. Overexpression of galectin-3 is associated with neoplastic transformation, enhancement of tumor cell adhesion to the extracellular matirx, and the subsequent metastatic spreading of cancer cells.