Rupp and Templin (2008) do a good job at describing the ever expanding landscape of Diagnostic Classification Models (DCM). In many ways, their review article clearly points to some of the questions that need to be answered before DCMs can become part of the psychometric practitioners toolkit. Apart from the issues mentioned in this article that are explicitly addressed in the article by Rupp and Templin (2008) there is one crucial issue that remains: equivalence of different DCMs, within or across different classes of DCMs. As DCMs claim to encode cognitive psychological theories, it is important that competing theories give rise to different models. That is, it should be possible to distinguish between competing theories on the basis of infinite observations. To the best of the authors' knowledge this issue has not yet been addressed. The situation is similar to that with the linear logistic test model (LLTM, Schleiblechner, 1972; Fischer, 1995) and the item response model with internal restrictions on item difficulty (MIRID, Butter, 1994; Butter, De Boeck, & Verhelst, 1998) that similarly try to encode substantive theories, and to the rotational invariance problem known from factor analysis. Since different, yet equivalent, models may lead to different diagnoses, and subsequently, different treatments, the problem is essential. This commentary addresses the equivalence problem. (Contains 1 footnote.)