Constitutional Economics - the analysis of constitutions drawing on the economic approach - has made important progress over the last two decades. The factors determining whether a constitution is complied with, however, have received only little attention. This is surprising, as a huge gap between constitutional text and constitutional reality seems to exist in many countries. In this paper, this gap is referred as the de jure/de facto gap. The paper discusses ways in which the gap can be researched systematically and surveys the scant available literature that has tried to do so thus far.