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The application of subsurface sensing to wood and wood-based materials is covered in four parts: (1) basic properties; (2) mechanical properties; (3) internal defects; and (4) adhesive bonding. The basic properties include moisture content, density, and grain orientation. Mechanical properties depend heavily on detection of basic properties, and emphasize those properties that are needed to predict strength in service. Internal defects relate to both green materials (trees and logs) and materials in service, primarily heavy dimension. Adhesive bonding includes both bond quality and bond formation. This review will address the determination of physical and mechanical properties of these materials; the detection of defects, both growth and processing; and the combined measurements to determine the conditions of such materials in various stages of processing or end-use. Subsurface sensing of wood and wood-based materials can be defined as any technique to acquire properties of these materials in a non-invasive manner and therefore will be considered similar to nondestructive evaluation.