This Geotechnical Technical Guidance Manual (TGM) provides technical guidance for geotechnical work performed by the Federal Lands Highway (FLH). It provides guidance for understanding and applying policies, standards and criteria in recognition of the need to manage financial and public safety risk and accomplish the missions of FHWA, FLH and partner agencies. Specific topics include geotechnical reconnaissance, site and subsurface investigation, analysis and design, reporting, PS&E involvement, construction support, performance monitoring, emergency response and consultant roles. The guidance in this TGM supports the policies, standards and standard practices presented in Chapter 6 of the Project Development and Design Manual (PDDM). Additionally, the TGM provides guidance for activities where standards and standard practices do not exist and it provides access to and guidance for the use of new technologies. Chapter 6 of the PDDM is the source for general direction on "what" should be performed, whereas guidance herein provides recommendations and options for "how" to perform these tasks. Like the PDDM, the TGM is intended to be used primarily as a web-based electronic reference document. Not all guidance is presented directly in the manual. When published sources present guidance that satisfies the requirements of FLH, or does so with only minor modification required, the TGM provides citations and links to those sources. If necessary, commentary on the application of these sources is provided here. This is done to keep the TGM small and more manageable, and also to allow easy and timely incorporation of new guidance as it is developed and published by FLH, FHWA and others. Technical guidance references cited and linked in this manual are classified as either "Primary," or "Secondary." Primary sources either present preferred guidance on how to accomplish a task or, when equal guidance is available through many sources, the Primary source is most widely available. "Secondary" sources are additional documents that are often relied on for FLH work; they present guidance to augment the Primary source. The PDDM presents work requirements through the official statement of policy and standards so it is an essential companion manual to the TGM. The TGM does not stand alone; policies and standards are repeated here only as necessary to offer guidance on their application. If discrepancy in the statement of policy or standards exists, the PDDM has precedence. Division-level documents also exist within FLH to provide guidance on unique technical practices or procedures at FLH Divisions; where these exist they should be followed for work within that Division. Also, although the organization of each of the Divisions is similar, there are differences. For this reason, the project delivery process and how the Geotechnical Discipline works within that process is described largely at the Division level.