Matthews, a professor of engineering psychology at West Point, believes that a better grasp of how humans understand and adapt to their environments would improve the selection and preparation of fighters in armed forces. Psychology is also a critical part of caring for veterans coping with disabilities or posttraumatic stress disorder, and psychology’s insights might help reduce the alarming rates of suicide among Americans who have fought in Afghanistan and Iraq. But Matthews warns against assuming that all combat is psychologically damaging. And he forcefully argues that the U.S. armed forces must continue to move away from being predominantly white, male, and homophobic. He also notes that the U.S. military has benefited from a greater appreciation of the cultures in which it operates and from teaching its officers how to lead in complex settings. He concludes with some thoughts about how psychology might promote peace and on the ethical issues raised by providing psychological support to armed forces when they are doing bad or foolish things: he warns, for example, that psychologists should have nothing to do with torture. Although the book is somewhat U.S.-centric, Matthews’ style is engaging and draws extensively on his own experiences.