Galectins are glycan-binding proteins implicated in intracellular signaling, cell cell communication, cellular proliferation and survival. These endogenous lectins have emerged as key players in the tumor microenvironment. They are expressed and released by different cell types, including tumor, stromal, endothelial and immune cells. Galectins critically influence tumor progression by modulating tumor cell migration, invasiveness, angiogenesis and antitumor immune responses. Intracellularly, galectins modulate survival and proliferation and they interact with a variety of signaling pathways.