Nutrition of the gilt and the sow has evolved rapidly over the past 20 years. The importance of formulating diets according to genetic potential and production level is now recognized. This recognition has arisen from research addressing problems at a factorial and mechanistic level as well as from models integrating the last 20 years of empirical data. This chapter covers applied and biological aspects of nutrition for the replacement gilt, gestating, lactating, and dry sow. Feeding practices at each production stage have specific objectives. However, because of the interrelation between each production stage, feeding practices must be geared to a long-term beneficial reproductive outcome. The way the replacement gilt is nutritionally managed during growth will impact reproductive longevity. Feeding of pregnant sows is not only concerned with optimizing fetal survival and growth but also with maximizing voluntary feed intake during lactation. While the short-term objective of feeding lactating sows is to maximize litter growth rate, the long-term objective is to minimize the weaning-to-estrus interval during the dry period and maximize ovulation rate for the following pregnancy. These issues are discussed using the current literature with an emphasis on nutrient requirements.