David Brooks recently wrote an interesting piece in the NY Times documenting the flow of immigrants into English-speaking countries (e.g., the United States, United Kingdom, Australia, Canada and New Zealand). Perhaps the most interesting aspect of his op-ed is his discussion of middle-class immigrants. Workers in the poorest countries of the world do not have the resources to migrate, while upper-income workers have little incentive to migrate. The majority of recent worldwide migrant flows originate in developing countries that are experiencing economic growth and hence growing middle classes (notable examples are China and India). Income is an important push factor for immigrants (as discussed in Chapter 2), and as countries develop, more workers have the resources and aspirations to migrate abroad.