After reading the last 12 chapters, it has probably become apparent to you that virtually everything associated with the concept of intelligence, including its conceptualization and measurement, is fraught with controversy. However, the topic of group differences in intelligence is particularly treacherous for researchers and anyone who writes about differences. Here is the one statement that scientists and others concerned with group differences in intelligence can agree on: There are some group differences, on average, on some tests that purportedly measure intelligence. This may be the only statement that we make in this chapter that goes unchallenged. The way we answer questions about group differences in intelligence is both personal and political. Every person belongs to many groups – racial, ethnic, language, country of origin, religious, gender, age, rural–urban, and many more. Even though we will be very careful when discussing differences to emphasize that the questions are about average differences among groups, these statements quickly become interpreted as statements about every member of the group, and readers may become defensive or prideful depending on their own group membership. The way we understand the extent of and reasons for these group differences has important social implications. Is there little overlap between two groups or are the group means so close together that the average difference has little or no meaning? If we think of group differences as large, then we could justify different treatment for members of different groups, perhaps in education, affirmative action, social welfare programs, parenting practices, and in other ways.