Pairwise testing is a powerful technique for generating software test configurations and test data. Compared with random test case selection, pairwise designs can provide better coverage with fewer test cases. Pairwise designs can lead to more effective testing, for improved quality and cost savings. This guide gives practicing software engineers a concise summary of pairwise testing. Several examples illustrate designs for configurations, input values, database tables and state model transitions. Together they provide a quick reference for how similar problems can be analyzed and what considerations go into effective test designs.