This chapter provides injury researchers with a guide to the methodologic standards for developing high-quality clinical decision rules. It also serves as a guide to help readers critically appraise the methodologic quality of a paper or papers describing a clinical decision rule. The chapter considers the six major stages in the development and testing of a new clinical decision rule and discusses a number of standards within each stage. It uses examples from injury care and from the own research on clinical decision rules for radiography in trauma. Few clinical decision rules have been successfully derived, validated, and adopted into clinical practice. This is because development of an effective decision rule is an expensive process. Medicine has many clinical situations which would benefit from a decision rule and this provides many research opportunities. This chapter outlines important methodologic issues for both the critical reader and the clinical researcher to consider.