Ground penetrating radar is a geophysical survey method widely applied to the assessment and monitoring of cultural heritage buildings. It is commonly used as a method of structural evaluation because it is nondestructive and noninvasive. This chapter describes the historical development of the method and explores the fundamentals and theory of ground penetrating radar systems and the properties of electromagnetic waves. Furthermore, it discusses some of the main applications and explains the procedure for data processing. Finally, it presents several case studies in the cultural heritage of Portugal and Spain.