Biological materials are omnipresent in the worldaround us. They are the main constituents in plant and animal bodies and have adiversity of functions. A fundamental function is obviously mechanicalproviding protection and support for the body. But biological materials mayalso serve as ion reservoirs (bone is a typical example), as chemical barriers (likecell membranes), have catalytic function (such as enzymes), transfer chemicalinto kinetic energy (such as the muscle), etc.This lecture will focus onmaterials with a primarily (passive) mechanical function: cellulose tissues(such as wood), collagen tissues (such as tendon or cornea), mineralizedtissues (such as bone, dentin and glass sponges). The main goal is to give anintroduction to the current knowledge of the structure in these materials andhow these structures relate to their (mostly mechanical) functions.