The increasing power of personal computers has e:ncouraged a proliferation of building energy simulation software packages. The prospective user has no way to quantitatively judge the appropriateness of a given software package for a given design problem. To address this issue, the Building Energy Simulation Test (BESTEST) procedure was developed for systematically testing whole building energy simulation programs and diagnosing sources of predictive disagreement. The BES TEST procedure takes a "comparative testing" approach where a program is compared to itself or to other programs.