How Many Is Too Many?: From the stony streets of Boston to the rail lines of California, from General Relativity to Google, one of the surest truths of our history is the fact that America has been built by immigrants. The phrase itself has become a steadfast campaign line, a motto of optimism and good will, and indeed it is the rallying cry for progressives today who fight against tightening our borders. This is all well and good, Philip Cafaro thinks, for the America of the past—teeming with resources, opportunities, and wide open spaces—but America isn’t as young as it used to be, and the fact of the matter is we can’t afford to take in millions of people anymore. We’ve all heard this argument before, and one might think Cafaro is toeing the conservative line, but here’s the thing: he’s not conservative, not by a long shot. He’s as progressive as they come, and it’s progressives at whom he aims with this book’s startling message: massive immigration simply isn’t consistent with progressive ideals. Cafaro roots his argument in human rights, equality, economic security, and environmental sustainability—hallmark progressive values. He shows us the undeniable realities of mass migration to which we have turned a blind eye: how flooded labor markets in sectors such as meatpacking and construction have driven down workers’ wages and driven up inequality; how excessive immigration has fostered unsafe working conditions and political disempowerment; how it has stalled our economic maturity by keeping us ever-focused on increasing consumption and growth; and how it has caused our cities and suburbs to sprawl far and wide, destroying natural habitats, driving other species from the landscape, and cutting us off from nature. In response to these hard-hitting truths, Cafaro lays out a comprehensive plan for immigration reform that is squarely in line with progressive political goals. He suggests that we shift enforcement efforts away from border control and toward the employers who knowingly hire illegal workers. He proposes aid and foreign policies that will help people create better lives where they are. And indeed he supports amnesty for those who have, at tremendous risk, already built their lives here. Above all, Cafaro attacks our obsession with endless material growth, offering in its place a mature vision of America, not brimming but balanced, where all the different people who constitute this great nation of immigrants can live sustainably and well, sheltered by a prudence currently in short supply in American politics.