Resumen:
Between February 1949 and the fall of 1957, Opus Dei in the United States went from a small group of five pioneers, based in Chicago, to one hundred and fifty members with centers in six cities in the Midwest and on the East Coast. This article focuses on the apostolic work of the men of Opus Dei and endeavors to establish the timeline, geography, and the demographics of this period. The article also seeks to address some of the institutional dimensions of these beginnings. Three stages are observed: the beginnings (1949-1953), the first maturity (1953-1955), and the growth that gave way to the division into two Regions (1955-1957).