Wood is a ubiquitous material used throughout history as fuel for cooking, heating, weapons and ships, construction, and furniture. Today wood is often seen more as an aesthetic than a structural choice, but pound for pound, white oak can be stronger than mild steel. Building with wood requires a sound knowledge of its physical structure and chemistry. And from one region to the next the wood chosen for different activities differs based on the available species. In preservation, it is important to understand why particular woods were originally selected for various functions in a building and how they were variously joined to function as a larger structural system. Before repairs are contemplated, the original design and materials, their strengths and weaknesses, and the repairs and deterioration that have resulted must all be understood.