Hartmann (Psychiatry/Tufts Univ. School of Medicine; The Functions of Sleep, 1973) writes accessibly and persuasively about ``boundaries''—his way of conceptualizing the mind. Hartmann makes a strong and eloquent case for the validity of boundaries as a psychological tool. In the course of his extensive studies on nightmares, he tells us, he encountered many aspects of subjects' lives that couldn't be explained—a quandary that led him to conceive of ``thick'' and ``thin boundaries,'' and, ultimately, to develop his ``Boundary Questionnaire,'' reproduced here. The result is a ``mental map,'' deriving its terms from common sense and experience as well as from classical psychology and psychoanalysis. Boundaries pervade our lives, Hartmann says, informing every detail of the way we exist in both waking and sleeping states—determining how ``open'' we are to experiences both inner (issues of self) and outer (relationships of all kinds). While Hartmann draws on extremes of ``thick'' and ``thin'' to make his points, most of us fall somewhere in between. He claims no definitive answers to the ``nature versus nurture'' question, but boundaries do appear to change in reaction to environmental factors, though not always in adaptive ways. The author concludes by pointing to the practical clinical value of boundaries in psychotherapy (individual, couple, and group) and psychopathology, as well as indirectly in the treatment of many medical and psychological conditions. It's a concept with much potential for the ongoing study of personality, the mind, and the organization of the brain. Never reductive, Hartmann sketches an insightful map of the mind that may prove of use to professionals and laypersons alike in the endless quest ``to know ourselves.''