In order to produce a new generation of green buildings, it will be necessary to clearly identify their performance requirements, and to assure that these requirements are met. A long-term goal is to provide building decision-makers with the information and tools needed to cost-effectively assure the desired performance of buildings, as specified by stakeholders, across the complete life cycle of a building project. A key element required in achieving this goal is a method for explicitly documenting the building performance objectives that are of importance to stakeholders. Such a method should clearly define each objective (e.g., cost, energy use, and comfort) and its desired level of performance. This information is intended to provide quantitative benchmarks useful in evaluating alternative design solutions, commissioning the newly constructed building, and tracking and maintaining the actual performance of the occupied building over time. These quantitative benchmarks are referred to as performance metrics, and they are a principal element of information captured in the Building Life-cycle Information System (BLISS). An initial implementation of BLISS is based on the International Alliance for Interoperability's (IAI) Industry Foundation Classes (IFC), an evolving data model under development by a variety of architectural, engineering, and construction (AEC) industry firms and organizations. Within BLISS, the IFC data model has been extended to include performance metrics and a structure for archiving changing versions of the building information over time. This paper defines performance metrics, discusses the manner in which BLISS is envisioned to support a variety of activities related to assuring the desired performance of a building across its life cycle, and describes a performance metric tracking tool, called Metracker, that is based on BLISS.