DEFINITIONS We have been liberally using the term ‘smart materials’ without precisely defining what we mean. Creating a precise definition, however, is surprisingly difficult. The term is already in wide use, but there is no general agreement about what it actually means. A quick review of the literature indicates that terms like ‘smart’ and ‘intelligent’ are used almost interchangeably by many in relation to materials and systems, while others draw sharp distinctions about which qualities or capabilities are implied. NASA defines smart materials as ‘materials that ‘‘remember’’ configurations and can conform to them when given a specific stimulus’,3 a definition that clearly gives an indication as to how NASA intends to investigate and apply them. A more sweeping definition comes from the Encyclopedia of Chemical Technology: ‘smart materials and structures are those objects that sense environmental events, process that sensory information, and then act on the environment...