This synthesis will be of interest to pavement, highway, and geotechnical engineers, and others interested in pavement structural design practices. Information is provided on flexible and rigid pavement design, design elements common to flexible and rigid pavement, and flexible and rigid pavement overlay design. Additionally, the synthesis discusses pavement research currently underway and recently completed by researchers of the United States and Canada. The structural design of flexible and rigid pavements has evolved from the application of engineering judgement to include a variety of processes. This report of the Transportation Research Board describes the various methods for structural pavement design in the United States and several Canadian provinces. Only the structural aspects of design are considered, i.e., those intended to provide strength or stiffness to the pavement. The functional aspects of design (such as skid resistance), are not considered.  The report for this topic can be purchased at https://www.trb.org/news/blurb_detail.asp?id=3368