This chapter analyses the evolution of Ethiopian legal systems from traditional customs to formal codification. It traces the decline of Aksum and the period of Zagwe rulers, noting nevertheless the scarcity of legal sources from this period. It examines the Ethiopian legislation during the Emperor Amdä Ṣǝyon’s reign, which marked a turning point with the creation of Śǝr’atä Mängǝśt, an early legal text governing court rituals and imperial administration. The study focuses then on the most notable legal milestone, the adoption of the Fǝtḥa Nägäśt, which draws from biblical, Byzantine, Roman, and Islamic sources across its twenty-two ecclesiastical law and twenty-nine secular law chapters. It examines the code’s detailed marriage regulations, including procreation emphasis and bigamy prohibitions. The study explores how imperial courts applied the Fǝtḥa Nägäśt, with its strict Christian rules concerning monogamy and age limits for marriage, alongside customary laws. This dual legal system enabled practices such as temporary marriages (dämoz) and marriage by abduction (ṭäläfa) to persist despite formal prohibitions, which demonstrates selective law enforcement and the enduring impact of unwritten traditions in Ethiopia.