The 1931 Constitution of Ethiopia was the first modern constitution of the Ethiopian Empire, intended to officially replace the Fetha Nagast, which had been the supreme law since the Middle Ages. It was promulgated in "an impressive ceremony" held 16 July 1931 in the presence of Emperor Haile Selassie, who had long desired to proclaim one for his country. In the preface to his translation of this constitution into English, William Stern writes, "this was the first instance in history where an absolute ruler had sought voluntarily to share sovereign power with the subjects of his realm." This statement, however, is not completely accurate, as the adoption of a constitution was somewhat pressed by international opinion.In virtue of this constitution, Ethiopia, one of the last absolute monarchies still existing, began the process of constitutionalization of imperial institutions, grounding the Emperor's authority on more solid basis, but also allowing some initial forms of limitation and participation; this evolutive process would continue after World War II with a new constitution.

The emperor of Ethiopia (Ge'ez: ንጉሠ ነገሥት, nəgusä nägäst, "King of Kings"), also known as the atse (Amharic: አፄ, "emperor"), was the hereditary ruler of the Ethiopian Empire, from at least the 13th century until the abolition of the monarchy in 1975. The emperor was the head of state and head of government, with ultimate executive, judicial and legislative power in that country. A National Geographic article from 1965 called imperial Ethiopia "nominally a constitutional monarchy; in fact [it was] a benevolent autocracy".