Seligman uses a workmanlike writing style to convey some significant results of his and others' psychological research on the phenomenon of "learned helplessness," a state where people and dogs and other things just give up on some task, or even die in some cases. Each chapter has a thesis that is supported by a litany of studies, and, as you might expect, these theses walk through the phenomena of depression, development, and death.
If you or someone you know is depressed and you want to know more about why and how depression happens, this book is fantastic (and hard to get, apparently).