In just 6 years, Early Head Start has grown from 68 initial grantees to some 650 programs and, by early 2001, was serving more than 55,000 families with infants and toddlers throughout the country. With an increasing share of the federal Head Start budget, Early Head Start is an ambitious effort in which the Administration on Children, Youth and Families (ACYF) is responding to the "quiet crisis" facing infants and toddlers in this country, as identified by the Carnegie Corporation of New York in its 1994 Starting Points. This overview to the special issue of the journal describes the program, its growth, and the changing policy and program environment of its first 5 years; explains how the federal and regional infrastructure supports Early Head Start through training, technical assistance, and monitoring; summarizes the design and conduct of the national evaluation and local research studies; presents the key lessons that the research has yielded so far; and concludes with an assessment of the challenges that lie ahead for creating a solid base of knowledge for programs serving low-income families with infants and toddlers.RESUMEN: El programa "Early Head Start" se inició otorgando becas y subsidios a 68 programas, y se ha expandido hasta llegar a ayudar a 650 programas que, para principios de 2001, prestaban ayuda a más de 55,000 familias con infantes pequeños por todo el país. Con el incremento de dinero en el presupuesto federal de "Head Start," el programa "Early Head Start" representa un enorme esfuerzo por medio del cual la Oficina para la Administración de Asuntos de los Niños, la Juventud y la Familia (ACYF) responde a la poco conocida crisis a la que se enfrentan los infantes de este país, tal como ha sido identificada por la Corporación Carnegie de Nueva York en su publicación de 1994 Starting Points (Puntos de partida).