The design of a safe transportation system requires numerous design decisions that should be based on data acquired by rigorous scientific method. Naturalistic data collection and analysis methods are a relatively new addition to the engineer's toolbox. The naturalistic method is based on unobtrusively monitoring driver and vehicle performance under normal, everyday, driving conditions; generally for extended collection periods. The method generates a wealth of data that is particularly well-suited for identifying the underlying causes of safety deficiencies. Furthermore, the method also provides robust data for the design and evaluation of safety enhancement systems through field studies. Recently the instrumentation required to do this type of study has become much more cost effective allowing larger numbers of vehicles to be instrumented at a fraction of the cost.This paper will first provide an overview of the naturalistic method including comparisons to other available methods. The focus of the paper then shifts to review the evolution of the data acquisition systems (DAS) and methods that have enabled naturalistic data collection. The goal is to provide readers with an understanding of how technology and unique partnerships has allowed the naturalistic data collection method to mature.