Much of everyday experience takes place beyond the range of our senses. And in our contemporary predicament, where so much seems beyond personal control, what is invisible generates an index of what we are. A Field Guide to the Invisible is a layperson's guide to the inescapable stew we're in, a thought-provoking catalog of life's ingredients that are literally out of sight and therefore too often out of mind.

In medieval times, everyone knew the air was rife with menacing spirits - the souls of unbaptized babies, graveyard ghouls, winged demons who could rip the unwary from the world of the senses.

In our own age of chronic low-dose exposure to sundry radiations, of infections from exotic microbes, of habitats where the sources of stress are amorphous, of a biosphere so radically changed by the hand of man that the natural protections it once provided are no longer assured, it is still the invisible that worries us most. A Field Guide to the Invisible maps points in a parallel world, ignored at our peril, that we inhabit simultaneously with the one before our very eyes.