Adequate and balanced nutrition is essential for the survival of preterm infants and, more importantly, for improving their short- and long-term health outcomes. In this population, mother’s own milk is the first choice because it reduces all-cause mortality and improves long-term neurodevelopmental and cardiovascular outcomes. When mother’s own milk is not available, donor human milk is the second choice, as long as this alternative is possible. Fortification of human milk, either Mother’s own milk (MOM)mother’s own milk or donor human milk, with a multi-nutrient fortifier is strongly recommended for infants born at less than 32 weeks. Standard fortification is the most used fortification method in clinical practice and consists of adding a fixed amount of multi-nutrient fortifier to given of human milk volume. Although this method has advantages over the non-fortified human milk, it may not be sufficient to meet the nutritional needs of the growing preterm infant. Alternatively, two individualized fortification methods have been used: adjustable and target. In adjustable fortification, modular protein is added to the standard fortified human milk when low blood urea nitrogen levels indicate insufficient protein intake. In target fortification, the macronutrient content of the human milk is measured periodically to guide the possible addition of modular macronutrient supplements to the standard fortified human milk in order to more accurately achieve the recommended nutrient targets. Both methods of individualized fortification have been reported to result in improved growth in very low birth weight infants, compared to standard fortification. Body weight, length and head circumference growth rates are considered the more sensitive anthropometric measures for monitoring nutritional interventions in preterm infants. During the first postnatal weeks, the initial and transient weight loss should be considered when interpreting nutritional assessments. Assessment of changes in fat mass, fat-free mass, and percent fat mass over time provides a valuable indication of the quality of growth in preterm infants.