This book provide investigation of the most applicable geophysical tools (microgravity, electric resistivity, and ground penetrating radar) from the standpoint of detection of subsurface cavities. The book is presented in 5 chapters Chapter 1, explain the term "subsurface cavity" and describes the problem posed by its existence in the environmental and engineering works, and introduces the early applications of the geophysical methods in this respect focusing on the most efficient methods. Chapter 2, introduce the microgravity technique and presents, develop, and analyse four interpretation techniques used to determine the cavity location from the residual gravity data. Chapter 3, presents the basic concepts and applications of the resistivity methods to cavity detection and site investigation, presents it's application to six engineering sites representing different geologic environments. Chapter 4, describe the basic concepts and applications of the ground penetrating radar method especially in the field of cavity detection and site investigations, providing field example from engineering sites. Chapter 5, Presents the conclusions.