This report gives an overview and summarizes the results of the research conducted under the four geotechnical projects established during the 1970's. It describes the efforts and results of 25 years of research spanning three decades from 1973-1998. The main purpose of the report is to provide a summary of the FHWA geotechnical research activities over the last quarter of the 20th century. It is intended for the general engineers and administrative managers of FHWA and the SHA's. Also presented are descriptions of the various problems that were addressed; and the report discusses the objectives and scope of each project in detail, except for the Tunneling Project, which is reported elsewhere (see appendix B). A review of each project's organization and approach is presented before the results are noted and evaluated. Technology transfer and future research needs are also covered separately to highlight the important nature of each topic.