When one picks up a multiauthored book in a series like this, one wonders what will be distinctive about its contents. one wonders about the "Concept of Symbiosis. " does it have the same meaning for all authors and all potential readers? one is further tempted to question the concept of stress. What is the meaning of the c- cept of stress? Some change in the biotic or abiotic aspects of the environment or habitat of the symbiotic partners? many might support the more general def- tion of symbiosis credited to de bary (1879), that symbiosis is the living together of separately named organisms. Something like Smith's (1992) more restricted PoLLnPia (P ermanent or Long-Lived intimate associations between diffe- ent organisms, usually of different sizes, in which the larger organism, the host, exploits the capabilities of one or more smaller organisms) seems to be a better ft for a book centered on the effects of stress on symbiosis. PoLLnPia implies an integrated holobiont system that has adapted itself to living successfully in a particular environment that could be construed as harsh for nonsymbiotic s- tems. often, when queried for examples, one thinks of lichens, of corals living in oligotrophic tropical waters, of Pompeii worms living in association with che- lithotrophic bacteria, and of all sorts of herbivorous animals living in associations with microorganisms. Presumably, the hosts could not survive, or thrive, in their habitats without their smaller partners doing their trophic work for their holo- otic systems.