Lactoferrin is the second most abundant whey protein in human milk and is known for its functional benefits, particularly antimicrobial activities. We report a comprehensive evaluation of the published literature on quantitative changes in lactoferrin in term and preterm human milk through the course of lactation. We also considered methods used to quantify lactoferrin. We critically evaluated 94 articles on human milk with 52 meeting study inclusion criteria (2724 women). A descriptive analysis of the data was performed. Lactoferrin concentration was highest during early lactation and rapidly declined to remain relatively unchanged from 1 month to 2 years of lactation. The unweighted mean of mean (±SEM) concentrations of lactoferrin in early milk (<28 days lactation) was 4.91 ± 0.31 g/L (range of means 0.34-17.94 g/L; median 4.03). For mature milk, the mean of means was 2.10 ± 0.87 g/L (range of means 0.44-4.4 g/L; median 1.91). The majority of data were derived from Europe with fewer studies from Africa and South America. There was a paucity of data on preterm milk. This comprehensive dataset explains in detail the longitudinal changes of lactoferrin concentrations in human milk throughout the world and briefly describes factors that may influence these concentrations.