In this article we describe new research to investigate unintended pregnancies during the transition to adulthood. The Relationship Dynamics and Social Life (RDSL) study begins with a 60-minute in-person interview about family background and current relationship characteristics. At the conclusion of the interview, respondents are enrolled in an ongoing journal, which consists of a 5-minute survey via web or phone and occurs weekly for 2.5 years. We have enrolled over 1,000 young women in the study and have experienced excellent baseline response rates and high journal participation rates. Below we describe the limitations of past research on unintended pregnancy as a background for our study. Then we provide a detailed description of the study and its design strengths and weaknesses.