Wood is one of the most intriguing structural materials and the only one that is truly renewable. Along with stone, wood is the oldest structural material on the planet and has been extensively used throughout human history. Due to its aesthetical value and positive environmental impact, wood has experienced a renaissance in construction. As a biodegradable, hygroscopic, non-isotropic material, wood presents special challenges for a professional working with it and requires thorough knowledge ranging from biology to continuum mechanics. This state-of-the-art report reflects the current knowledge in the area of in situ assessment of the physical and mechanical properties of wood structures. Nondestructive, semi-destructive and destructive methods are described in a systematic manner where technology, equipment and limitations are discussed. Some of the discussed methods are used in other materials such as masonry and concrete. Most of the methods, however, are specific to wood and special qualifications are required to understand and apply these methods effectively. Existing methods are constantly improved and new methods are being developed. This report includes methods that are used in practice or have shown significant promise and have a body of knowledge that supports statements made in this report. This is a useable tool for professionals, researchers, educators and students.