With his classic book Why We Get Sick, Randolph Nesse established the field of evolutionary medicine. Now he returns with a book that transforms our understanding of mental disorders by exploring a fundamentally new question. Instead of asking why certain people suffer from mental illness, Nesse asks why natural selection has left us all with fragile minds. Drawing on revealing stories from his own clinical practice and insights from evolutionary biology, Nesse shows how negative emotions are useful in certain situations, yet can become excessive. Anxiety protects us from harm in the face of danger, but false alarms are inevitable. Low mood prevents us from wasting effort in pursuit of unreachable goals, but it often escalates into pathological depression. Other mental disorders, such as addiction and anorexia, result from the mismatch between modern environments and our ancient human past. And there are good evolutionary reasons for sexual disorders and for why genes for schizophrenia persist. Taken together, these insights and many more help to explain the pervasiveness of human suffering, and show us new paths for relieving it. Good Reasons for Bad Feelings will fascinate anyone who wonders how our minds can be so powerful, yet so fragile, and how love and goodness came to exist in organisms shaped to maximize Darwinian fitness.