Book excerpt: This practice manual examines the Geotechnical Baseline Report (GBR) which establishes a contractual statement of geotechnical conditions anticipated during underground and subsurface construction. Emphasis is placed on large underground projects such as tunnels, underground chambers, shafts, subway stations, mine development, and deep foundation excavations that have a significant anticipated risk of differing site condition claims. Guidelines for what should be included in the GBR are provided, in addition to a checklist of items to consider, recommendations for the content and wording to be used in baseline statements to improve their clarity and precision, and examples of problematic and improved practice in stating baselines. The importance and benefit of ensuring compatibility between the GBR and other elements of the Contract Documents, with emphasis on the specifications, drawings, and payment provisions is also discussed.