There is a fundamental gap in our knowledge of the over 710,000 older adults residing daily in the 22,000+ assisted living (AL) facilities in the US. This is primarily due to our inability to identify AL residents with secondary data as we have for beneficiaries receiving services in nursing homes (NHs). The long-term goal of this research agenda is to study the changing landscape of long-term care (LTC) and to understand the role of AL in providing quality care to our nation's most at-risk elders in much the same manner previously done with NHs. Critical impediments to this goal is the lack of a national dataset of ALs, a methodology to identify and track AL residents' LTC trajectories, and an understanding of how changes in the AL market affects other LTC sectors. To address this problem, our main goals of this application include the collection of an updated national census of AL providers to validate a methodology for identifying AL residents using secondary data sources. The rationale that underlies this proposed re` search is that a national dataset of AL providers, a validated method to identify AL residents, and an understanding of the effect of the growth in the national AL market will, for the first time, allow researchers to investigate in more detail the national landscape of AL utilization and resident outcomes. The specific aims include: 1) To compile, geocode, match to other LTC data, and make publicly available a 2013 national dataset of AL providers on LTCfocUS.org, 2) To test the validity of a methodology for identifying AL residents against samples of Medicare beneficiaries receiving healthcare services within an AL and 3) To evaluate the effect of changes in the geographic supply of AL beds between 2007 and 2013 on the private-pay NH market. Our research is innovative because we will be the first to supply a national dataset of ALs and we put forward a new and unique approach to identify AL residents, namely the use of the 9-digit ZIP code reported in Medicare enrollment records, which we will validate by combining Home Health assessment data and Medicare Part B Place of Service Codes. In addition, we will improve our ability to identify the relationship of changing AL supply with the market for NH care by creating an innovative measure that captures the number of private-pay resident days in NHs on a national scale. Consequently, a better understanding of the effect of the changing AL market on NH private-pay occupancy and length of stay is expected to result. This work is significant because as more private, State, and Federal dollars are spent on AL, identifying users of these services, tracking their healthcare utilization and outcomes, and understanding the impact on other LTC market sectors becomes crucial. In addition, findings from this research have the strong potential for providing us the fist step in a continuum of research to be proposed in an R01 grant application following the completion of this work that is expected to elucidate provider quality, AL resident outcomes (e.g. hospitalization and NH placement), racial and ethnic disparities, and healthcare costs associated with this large, growing site of LTC.