Lactoferrin (LF), also known as lactotransferrin (LTF), is a multifunctional protein of the transferrin family. Lactoferrin is a globular glycoprotein with a molecular mass of about 80 kDa that is widely represented in various secretory fluids, such as milk, saliva, tears, and nasal secretions. Lactoferrin is also present in secondary granules of PMNs and is secreted by some acinar cells. Lactoferrin can be purified from milk or produced recombinantly.
Human colostrum ("first milk") has the highest concentration, followed by human milk, then cow milk (150 mg/L).

Lactoferrin provides antibacterial and immune-supporting activity to human infants. LF is a component of the immune system responsible for defense at the mucosal level, due to its high antimicrobial activity.

Lactoferrin is crucial to the increase in immune functions for breastfed infants. It is also believed to be widely important to maintaining immune functions further in life past infancy. It helps develop the gastrointestinal and immune system in newborns.