The American Community Survey (ACS) will be producing three- and five-year period estimates starting in 2008 and 2010, respectively. Before these are released the ACS has created a series of period estimates for research using the data in thirty-four counties from data collected in 1999-2005. These estimates were produced using the methods planned for 2008 and 2010. We will share our research results on the methods that the Census Bureau has developed to produce the multiyear estimates. There are four dimensions of the methodology that we will emphasize: the conceptualization of the estimates, the estimation process, changes in geographic definitions, and use of inflation factors for dollar- valued estimates.