Although constitutions lay out the fundamental principles by which countries are governed, identifying exactly which legal materials are considered constitutional is not straightforward. This is for two reasons. First, there is no systematic evidence about the relative importance of countries’ formal, written constitutions—the “Large-C” constitution—versus the broader body of constitutional law derived from sources like judicial decisions, treaties, and conventions—the “small-c” constitution. Second, it is often difficult to establish which legal materials are definitively part of a country’s small-c constitution. We investigate small-c constitutions using a global expert survey on the nature of constitutional rights protection to 188 experts from 103 countries. The results illustrate that Large-C constitutions are the primary source of constitutional rights in a majority of countries, but small-c constitutions also plays a significant role, especially in older constitutional systems.