The idea of measuring people's interests has been around since World War I, when military psychologists wrestled with the problem of how to determine which recruits should be cooks and which should be members of the cavalry. Most of us recognize that the type of man who likes the job of cooking (there were no women in the armed services in WWI) is different from the type of man who likes the job of riding and tending horses, and the idea of classifying people by their interests has some intuitive appeal. After WWI, it became clear to some of those same psychologists that the idea had important implications for civilians as well. If it were possible to measure people's vocational interests and to use those data along with information about abilities and values, it might be possible to perform two important, interrelated services.