An implicit element of many theories of constitutional enforcement is the degree to which those subject to constitutional law can agree on what its provisions mean (call this constitutional interpretability). Unfortunately, there is little evidence on baseline levels of constitutional interpretability or the variance therein. This article seeks to fill this gap in the literature, by assessing the effect of contextual, textual and interpreter characteristics on the interpretability of constitutional documents. Constitutions are found to vary in their degree of interpretability. Surprisingly, however, the most important determinants of variance are not contextual (for example, era, language or culture), but textual. This result emphasizes the important role that constitutional drafters play in the implementation of their product.