Parent-child cosleeping is typically considered by researchers and parenting advisors to be a unitary construct. However, existing evidence suggests that parents who purposefully sleep with their young children at night (intentional cosleepers) may be very different than those who co-sleep in reaction to existing sleep problems (reactive cosleepers). The object of the current study is to compare these two groups along three dimensions: demographics, sleep behaviors, and maternal attitudes toward sleep. Participants recruitment occurred through two parenting e-mail listservs; one considered mainstream and one devoted to attachment parenting. The survey was completed online and submitted electronically. Participants included 450 mothers in the United States (mostly White and well-educated) with a target child between the ages of 6 and 59 months who cosleeps at least occasionally. Reactive cosleepers and intentional cosleepers reported many differences in their children's sleep behaviors and their own attitudes about family sleep, but few demographic differences. Frequent all-night cosleeping and parental ideological endorsement of cosleeping characterize intentional cosleeping. Reactive cosleeping is characterized by reduced parental satisfaction. Reactive and intentional cosleepers both report shared beliefs with their partners and a select group of friends, but a definite lack of shared beliefs with other elements of their social support systems. The distinction between intentional and reactive cosleeping appears to be a valid and useful one. Researchers should be aware of the differences when studying sleep in families with young children.