This article was excerpted from the author's "Charting the Bumpy Road of Coparenthood: Understanding the Challenges of Family Life", published in 2007 by "ZERO TO THREE." In the "Families Through Time" longitudinal study, James P. McHale and a number of colleagues met with expectant couples and then followed the families when the infants were 3 months, 1 year, and 2 1/2 years old. Through interviews, questionnaires, and observation, the researchers examined the transition couples underwent as they attempted to build productive coparenting alliances, defined as those in which partners are communicating regularly with one another about child-related issues and decisions and are supporting one another's parenting efforts. One important set of findings was how parents' difficulties in building a strong coparenting alliance affected their child's development. This article describes findings related to the effects of coparenting solidarity (or lack thereof) on toddler social-emotional development.