Central to attachment theory is the postulation of an inborn system to regulate attachment behavior. This system has been well studied in infancy and childhood, but much less is known about its functioning at later ages. The goal of this study was to explore the form and function of attachment behavior in the daily lives of young adults. Twenty eight days of online diary data were collected from a sample of 60 undergraduates. In addition to providing descriptive data on routine attachment behavior, the study tests the theorized function of attachment behavior--that is, affect regulation. With the exception of safe haven behaviors, results indicate that age-appropriate attachment behaviors are readily observable during this phase of development, tend to be preferentially directed toward attachment figures, and regulate affect in a theory consistent manner. Findings are discussed in terms of implications for normative developmental change and normative attachment processes.