Our society is becoming more complex, not just our personal lives. These two developments stem from many of the same causes, and reversing such trends does not seem feasible in either sphere. Indeed, with solemn mien politicians, preachers, futurists, and fanatics have told us so often that the world, in general, is becoming more complex that the idea seems commonplace. Nevertheless, in particular situations the meaning of this idea is often obscure: What do such pronouncements concretely mean, for instance, regarding the economy? Under what specific circumstances is the assertion true? Most importantly, how does it affect our daily lives?

I have written this book because I believe that the concept of complexity is crucial for understanding the evolution of the U.S. economic system. Defined precisely and used as a tool of quantitative research, it leads us to ask new questions about the economy, as well as to give us new answers to many old questions. It allows us to see how the population is becoming more heterogeneous, an important factor underlying the decline of social cohesiveness in the United States.