The Program for Climate Model Diagnosis and Intercomparison (PCMDI) at LLNL has developed a number of methods and tools for the diagnosis, validation and intercomparison of global climate models. Recently we have begun an independent appraisal of coupled model performance. The appraisal will focus on objective diagnostics including comparison of observations with "control run" simulations by several models. We plan to include both coupled and single-component (e.g., atmosphere only) model evaluations and -- with the permission of contributing modelers -- to make use of databases such as the Coupled Model Intercomparison Project (http://www-pcmdi.llnl.gov/cmip) and the Atmospheric Model Intercomparison Project (http://www-pcmdi.llnl.gov/amip). Our strategy is to evaluate coupled models as comprehensively as possible, and to develop and exploit new and innovative diagnostics. Results from our appraisal should help both to document the state of the art of climate modeling, including improvements over time, and to provide information relevant to developers seeking to improve their models.