This report is the first in a series of reports summarizing the results of the Residential Building Stock Assessment (RBSA). The RBSA is sponsored by the Northwest Energy Efficiency Alliance (NEEA) and is being conducted by Ecotope, Inc. with support by Ecova™, Delta-T, Inc., and ORC International. The primary objective of the RBSA is to develop an inventory and profile of existing residential building stock in the Northwest based on field data from a representative, random sample of existing homes. The RBSA establishes the 2011 regional baseline for housing stock for three categories of residences: single-family homes, manufactured homes, and multifamily homes. The results will guide future planning efforts and provide a solid base for assessing energy savings on residential programs throughout the Northwest.