The most promising techniques for non-destructive surveying of buildings are discussed in some detail. They include: x-ray and gamma-ray radiography, infrared detection, ultrasonics (to test for concealed inconsistencies and faults), microwave analysis (data interpretation is complex), magnetometry, fiber-optic surveying (viewing remote areas with an endoscope), and structural movement monitoring (surveying the behavior of cracks and fissures in masonry).