The notion of regular, full-time employment as one of the defining features of the U.S. economy has been called into question in recent years by the apparent growth of alternative or “nonstandard” work arrangements—part-time hours, temporary help, independent contracting, and other configurations. Identifying the extent of these arrangements, whether they are increasing and where they occur, is the first step to understanding their implications for the economy and the society. But such steps have been difficult to take because of the lack of appropriate data. Based on a national probability sample of U.S. establishments, the authors present estimates of the extent of these practices, evidence on changes in their use over time, and analyses that contribute to understanding why alternatives have come into play.