Infrastructures and buildings are built on a material that is heterogeneous in nature and whose properties are imposed by its origin: the ground. Soil or rock, the ground plays an important role in the cost and viability of any infrastructures and buildings during both their construction and their operation. Thus, knowing the ground and properly characterizing it, stands essential. This Book deals with the geotechnical engineering techniques and methods used to carry out a useful and successful study of the ground. Beginning by laying the foundations for a good geotechnical planning, which must be supported on the use of appropriate geological-geotechnical cartography,the Book shows the different techniques for terrain recognition and auscultation, addresses the geotechnical description of rock masses and summarizes the more common laboratory tests used in soils and rocks. All this based on the recommendations and principles given in relevant technical documentation such as the "Guía de Cimentaciones en Obras de Carretera" of Spain and the recommendations of the International Society for Rock Mechanics (ISMR).