Earthquakes are a serious threat to safety in multifamily apartment buildings and pose a significant potential liability to building owners. Multifamily buildings in 39 states are vulnerable to earthquake damage. Unsafe existing buildings expose multifamily building owners and tenants to the following risks: Death and injury of tenants, occupants, and visitors; Damage to or collapse of buildings; Damage to and loss of furnishings, equipment, and other building contents; Disruption of rental and occupancy functions and other building operations. The greatest earthquake risk is associated with existing multifamily buildings that were designed and constructed before the use of modern building codes. For many parts of the United States, this includes buildings built as recently as the early 1990s. Although vulnerable multifamily buildings need to be replaced with safe, new construction or rehabilitated to correct deficiencies, for many building owners new construction is limited, at times severely, by budgetary constraints, and seismic rehabilitation is expensive and disruptive. However, incremental seismic rehabilitation, proposed in this manual, is an innovative approach that phases in a series of discrete rehabilitation actions over a period of several years. It is an effective, affordable, and non-disruptive strategy for responsible mitigation actions that can be integrated efficiently into ongoing facility maintenance and capital improvement operations to minimize cost and disruption. This manual and its companion documents are the products of a Federal Emergency Management Agency (FEMA) project to develop the concept of incremental seismic rehabilitation-that is, building modifications that reduce seismic risk by improving seismic performance and that are implemented over an extended period, often in conjunction with other repair, maintenance, or capital improvement activities. It provides owners of Class A, B, or C multifamily buildings, be they Real Estate Investment Trusts (REITs), pension funds, partnerships, individuals, or other forms of ownership, with the information necessary to assess the seismic vulnerability of their buildings and to implement a program of incremental seismic rehabilitation for those buildings.