As an affluent person in a world of needy poor, I should probably do more to aid badly off persons around the globe. Many people subscribe to this thought, which prompts guilt and chagrin. However, the thought readily becomes an extremely demanding vise. If I am contemplating using a few dollars of mine to go to a restaurant and a movie, I might reflect that the money would do more good, yield more moral value, if I refrained from the personal expense and gave the money to a relief agency serving the global poor. Transferred to the relief agency, the money would save a life or prevent a severe deterioration in the quality of someone’s life. The vise tightens when I reflect further that if I give the few dollars to a relief agency, essentially the same decision problem recurs. I could contribute another similar increment of resources to a worthy cause and further reduce my expenditures to enhance my own quality of life. And another, and another, and so on. Peter Singer has observed that virtually all of us would agree that if we chance upon a child drowning in a pond we ought to save the child’s life even if the life-saving activity imposes a considerable sacrifice on us. We live in a world in which, in effect, children drowning in ponds or the moral equivalent are ubiquitous, and thanks to the existence of networks of...