The AASHTO Manual on Subsurface Investigations, Second Edition (2022), provides guidance on geotechnical subsurface investigations for transportation projects. The manual addresses the collection of subsurface data that engineers and planners use to identify, assess, and address risks associated with subsurface conditions, select design parameters, and monitor performance during construction and operation. Coverage includes drilling and sampling methods, illustrated in the manual by mud-rotary drilling and rig setups on difficult terrain, as well as in-situ testing techniques such as cone penetration testing. Geophysical methods are addressed as well, including electrical resistivity and magnetic survey techniques. Laboratory testing of recovered soil specimens, such as triaxial shear strength testing, supports the characterization of subsurface materials. The manual is intended for geotechnical engineers conducting and interpreting subsurface investigations for highway projects.