The American population has changed dramatically over the past several decades: fewer of us live in big families, more of us live alone or in pairs, and more of us favor metropolitan areas near the coasts. This Article proposes that our land use laws should affirmatively encourage the construction of infill housing that is, housing inside our built-up neighborhoods, of both cities and suburbs and that this infill should be apartment housing a form of living that has been disfavored under traditional land use law but is more popular among a changing American populace.