Lactoferrin is a multifunctional glycoprotein found in many body fluids. Although generally considered a component of the nonspecific host defense mechanisms, a variety of functions have been ascribed to lactoferrin. These include antimicrobial properties against a variety of organisms, roles in regulating myelopoiesis, hyposideremia, antibody synthesis, leukocyte cytotoxic activity and lymphocyte proliferation, antioxidant and prooxidant functions, growth promoter and inhibitor in nonlymphoid cells, and acting as a milk iron-transporter for the neonate. Many, but not all, functions of lactoferrin involve its iron-binding properties. Many functions also involve binding to or interacting with other macromolecules. Binding properties of lactoferrin for other proteins, glycosaminoglycans and other polysulfated substances, nucleotides, bacterial cell surfaces, leukocytes, and epithelial cells is reviewed, along with the functional implications of those binding interactions.