This dissertation compares the health-enhancing projects of lower- and middle-class U.S. women during pregnancy and postpartum. Current social stratification scholarship pays scant attention to the role of the body, while the literature on reproductive labor--which shows bodily carework to be a highly gendered activity--often disregards class. In my dissertation, I argue that the maternal body serves as a key site of class inequality at both structural and individual levels, simultaneously reflecting class differences and reproducing them through the techniques mothers adopt to cultivate their own health and their children's. Such projects (especially changes in diet and exercise) are common in mothers across racial/ethnic, socioeconomic, and geographic locations, even as their contents vary. Yet, while women's bodily practices may affect their physical wellbeing, such habits also are saddled with a range of social and moral meanings that are reinforced through the institutions in which mothers participate. Revealing the lie in oversimplified rhetorics of "good" versus "bad" mothers, my research shows how class mediates the near-universal efforts of new mothers to maximize their own health and their children's. Based on interviews and ethnographic observations I conducted with middle-class mothers and in offices of the federal Women, Infants, and Children (WIC) program in California and Florida, I present four main findings. First, WIC, a federal program for low-income women, aims to supplant traditional knowledge about the maternal body with medical authority. It also works to induct participants into what I call "neoliberal citizenship," emphasizing self-control and decreased reliance on public health services. Second, informal institutions popular among middle-class mothers--"mommy groups" and online message boards--offer members support and information, but also a space in which to assert mastery over body care habits and to engage in status contests with other mothers. Third, I suggest that differences in material, cultural, and institutional circumstances lead mothers to adopt divergent forms of agency with regard to the care of their bodies; while both groups in my study seek to make the right choices for their children's health and development, poor and working-class mothers' constrained choices tend to be misrecognized as lacking agency. Fourth, while recent research has fixated on mothers' self-care habits during pregnancy as determinants of children's physiological and developmental outcomes, I suggest that the modes through which they cultivate their children's bodies serve to transmit class-specific bodily knowledge and ethics, constituting children as classed subjects and reproducing both privilege and disadvantage across generations.