The 2007 AHAR represents an important milestone in HUD’s efforts to collect information and report on homelessness based on HMIS data from a nationally representative sample of communities. It is the first AHAR based on an entire year of data about persons who use emergency and transitional housing programs. This longitudinal information on homelessness is important for understanding the nature and scope of homelessness. It also provides a baseline for future reports that will provide direct year-to-year comparisons of the number and characteristics of homeless people and their patterns of service use. In addition, the report contains new information about the seasonal patterns of homelessness and long-term users of shelters and presents new appendices that provide community-level information on the number of homeless persons.