Postpartum depression is a serious health issue affecting as many as 10-15 % of postpartum women. This longitudinal study aimed to explore how psychological variables such as cognitive emotion regulation strategies, breastfeeding self-efficacy (BSE), and dimensions of social support predicted postpartum depressive symptoms (Edinburgh Postnatal Depression Scale). The data were collected with web-based survey questionnaires between May 2008 and December 2009, in a sample of 737 new mothers. The same questionnaire was surveyed at three points in time: 6 weeks, 3 months, and 6 months postpartum. Data were analyzed using multilevel modeling (level 1, time points; level 2, person). Results showed that BSE, certain cognitive emotion regulation strategies, perceived available support, and need for support predicted the rate of postpartum depressive symptoms. Only breastfeeding self-efficacy predicted change in postpartum depressive symptoms. This study illustrates the importance of psychological variables with regard to postpartum depressive symptoms. Implications for preventative efforts are discussed.