Despite the historical and contemporary significance of the Sharia, it has not yet been possible to solve the puzzle of its origins. Whereas previous research has postulated a greater or lesser degree of endogenous Islamic development, the present study reaches a different conclusion, namely that at the end of the 8th century Muslim state lawyers in Baghdad codified an Islamic “Imperial Law”, oriented strongly towards Roman-Byzantine law. It is part of an Islamic-Byzantine context, and can only be explained against this intercultural background.