The AASHTO Mechanistic-Empirical Pavement Design Guide: A Manual of Practice, Fourth Edition (2026), presents a pavement design methodology based on engineering mechanics validated with road test performance data. The manual walks through the stages of mechanistic-empirical design in sequence. These stages include selecting a trial design and a hierarchical input level, determining site conditions and factors, and establishing material properties and features of the pavement layers. The procedure then calls for executing the design in AASHTOWare pavement design software, followed by interpretation and analysis of the predicted performance. Separate guidance addresses trial design strategies for asphalt-surfaced and portland cement concrete-surfaced pavements. The guide is intended for pavement design engineers in agencies and industry who design and analyze new and rehabilitated pavement structures.