Over the last few years, many different types of sediment quality guidelines have been derived, and a debate has begun on how best to evaluate the predictive reliability of these guidelines. The reliability of sediment quality guidelines has important consequences for selection of specific guidelines for use, sampling designs, regulatory decision frameworks, and the extent to which biological testing is required to make decisions about dredging and cleanup actions. However, the authors of these studies are not all using the same terminology, the same definitions of errors and error rates, or the same methods of calculation. Definitions and general principles for determining the reliability of SQGs are proposed, to promote a common basis for discussion and comparison of the various SQGs available for use. Significant issues with current approaches to estimating reliability are also discussed.