noun
legal history; history of law
Academic discipline studying the historical development of legal systems and institutions.
彼は大学で法制史学を専攻している。
He is majoring in legal history at university.
法制史 is a more common term for legal history; 法制史学 explicitly refers to the academic study or discipline.
Compound of 法制 (legal system) + 史学 (historical studies).