Composite materials, or at least materials that could be regarded as composites, are widespread in nature. This is, of course, a reflection of the many gains in ‘efficiency’ that can be made by integration of two or more constituents. Moreover, the development of artificial composite materials, for mechanical and/or other purposes, has benefited considerably from insights gained by examining bio-composites, and by their direct utilisation. The kingdoms of both plants (wood, grasses, straw, etc.) and animals (bone, skin, teeth, marine shells, corals, etc.) offer many examples of highly successful materials that are essentially composites. Their importance relates not only to lessons about structure–property relationships, but also to the issue of degradation and recycling. While the ‘rotting’ of wood is often regarded as its Achilles’ heel, viable recycling strategies are increasingly required for all materials (and manufactured composites are often perceived as being unsatisfactory in this respect). It is clearly not appropriate in a book of this type to provide great detail about natural materials, or indeed about recycling, but a few of the main principles and issues involved are briefly summarised here.