Galectin-13 (Gal-13) is a lectin family member and is one of the prototype galectins. It contains one carbohydrate recognition domain (CRD), responsible for β-galactoside binding, and is biologically active as homodimers. Galectin-13 is expressed in the placenta, contributing to T cell apoptosis, immune regulation, and immune tolerance, which is indispensable for fetal development. For example, galectin-13 organizes crystal-like aggregates in the decidua, consequently attracting and killing maternal immune cells. Furthermore, galectin-13 is essential for driving neutrophil polarization in the placental-growth-permissive phenotype.