This manual is intended to provide a technical resource for geotechnical engineers responsible for planning and performing subsurface investigations so that project subsurface conditions can be characterized effectively and risks attributed to ground conditions can be identified and addressed. The manual is organized to reflect an emphasis on interpretation of geotechnical parameters for design and construction. It describes important considerations for planning and scoping of geotechnical investigations, means and methods for classification of soil and rock based on index property measurements, identifying and characterizing problematic soil and rock types for design and construction, guidance for interpretation of soil and rock properties from field and laboratory measurements, interpretation of geotechnical design parameters from individual measurements, identification and characterization of geotechnical hazards, and lastly, guidance for documenting and reporting results from geotechnical investigations.