It has been suggested that mother's milk has a more diverse flavor composition than infant formula milk as it reflects the maternal diet. This study aimed to identify volatile compounds in mother's milk and infant formula milks to obtain more knowledge about these sources of early sensory exposure in infant feeding. Mother's milk collected by ten lactating women, three times on three independent test days (n=90), and 11 different formula milks were examined. Formulas included seven milk-based liquid formulas and four powder formulas (one milk-based and three hypoallergenic). Both mother's milk and infant formulas were rich in lipid-derived volatile compounds including alcohols and carbonyl compounds. Formulas differed from mother's milk as they contained more volatiles related to thermal treatment such as methional, 2-furfural, and sulfides. By comparison, mother's milk revealed a higher variety of terpenes probably originating from the maternal diet. The number of identified volatiles in mother's milk varied both within samples obtained from the same woman and significantly between women. The latter one suggests large variety in breast-fed infants' exposure to volatiles. Qualitative differences existed for infant formulas. Powder forms revealed a greater number of compounds, predominantly secondary lipid oxidation products, and larger batch variations than liquid products. Extensively hydrolyzed formulas were significantly richer in volatile compounds associated with heat treatment of milk. These findings suggest that breast-fed infants are exposed to variations in volatile compounds in mother's milk, while formula-fed infants are exposed to less diverse flavors when fed infant formula from the same brand.