Past research in solid oxide fuel cell (SOFC) performance assessment and improvement has focused on cell operating voltage (efficiency). Related to this metric, but distinct and equally important, is performance degradation. This paper examines cell degradation, provides key definitions needed for its characterization, and discusses the relationship of various cell performance variables. To characterize degradation, two parameters are defined, namely, area-specific resistance (ASR), and degradation rate (DR). The ASR of a cell/stack increases as a result of degradation, and therefore needs to be modeled as a time-dependent parameter. A model for SOFC cell performance is used to describe polarization losses, and to predict degradation performance. The model is then used to demonstrate the use of ASR and DR in the assessment of degradation. Available experimental data is separately used to do the same. ASR is shown to be insensitive to certain variations in test conditions and therefore is the preferred parameter for fuel cell developers when comparing performance differences arising from incremental changes in design/materials. DR is the preferred parameter for determining changes in efficiency over the lifetime of the cell/stack, which is a key concern for end users. Published by Elsevier B.V.