This study seeks to give an account of the truth, scope, and validity of Calvin’s Christological understanding of the law in the light of his concept of Christus mediator legis. It sets out the key points of the intellectual origins of Calvin’s theology of the law, especially his study of law, Christ’s mediation of the law in the Old and New Testaments, and the relationship between the duplex office and the triplex use of the law. A comparative study between Calvin and contemporary Reformers–Luther, Bucer, Melanchthon, and Bullinger–and Servetus is made in order to point up the unique feature of the coherence between Christology and soteriology in Calvin’s theology of the law.