The year 2010 is special for science and society in the United States because the federal government is going to conduct its Decennial Census of Population, mandated in Article 1 of the Constitution. It will cost upwards of $15 billion and employ roughly 800,000 people for a short time. The Census of Population has been a critical data base for all of the sciences of our society, e.g., political science, sociology, economics, demography, and public health. Almost all of the population information that is used by the social sciences is based on the Census. Nearly every household survey conducted by the federal government (and many state, local, and private organizations) on topics as diverse as education, health, transportation, energy, and unemployment is based on census data. Following the 2000 Census, it was decided that the Census “long form,” which collected detailed household information on a fraction of the population, would be replaced by the American Community Survey (ACS), an extremely large complex monthly survey. Thus, with little fanfare, the ACS has become the critical foundation for understanding multiple aspects of our dynamic society. It samples about 3 million households per year and interviews the occupants to learn the detailed information that was, up through 2000, collected in the Census itself. This symposium will explore the relationship between the “old” Census and the “new” ACS as the basis for the social sciences.