The question “How does it work?” is the motivation of many physicists. Condensed matter physics, chemical physics and nuclear physics can all be thought of as descriptions of the relation between structure andproperties. The components of a biological system havefunctionalproperties that are particularly relevant to the operation of the system. Thus it is especially important in biology to understand the relation between structure andfunction. Such understanding can be sought at the level of the molecule, the cell, the organ, the organism or the social group.