This chapter introduces common methods of site investigation and discuss engineering issues related to different types of rock mass. Some sites may present geologic conditions where soil cover is either thin or absent and where observations of outcrops reveal all the rock types and structures. Desk study is the first step of investigation when all relevant information, including aerial photos and maps, is collected and analyzed. Field investigations are carried out in accordance with the relevant standard that clearly outlines the field procedures. Field work typically includes boreholes, site testing and seismic exploration. Boreholes are an important part of site investigation as they provide information about the geological settings of the area. Rock exploration can be done relatively quickly and inexpensively by means of seismic methods. Cross-sections provide important data on the geological conditions existing at the project site, including the type of rock, boundaries between different units and ground water.