This article provides an introduction and background to the Neonatal Intensive Care Unit Network Neurobehavioral Scale (NNNS). First is a summary of the history of the field of infant assessment. This is followed by a description of the NNNS, including its basic features and how the NNNS differs from other examinations. We then describe the biobehavioral basis for the examination and review studies in which the NNNS has been used. Finally we discuss the developmental model on which the NNNS is based and consider the implications of using the examination.