The present article explores Paul’s use and meaning of the διαθήκη (diathēkē, “covenant” or “testament”) in Galatians 3–4, as well as the relation between the covenants mentioned or presupposed in these chapters: the Abrahamic promise covenant, the Mosaic law covenant, and the Davidic and eschatological (“new”) covenants. The article first highlights elements that suggest that “covenant” is an important aspect of Paul’s biblical-theological argument in Galatians. Two sections develop the content of these covenants. In the final section, the relation between the covenants is brought to bear upon the covenant and Mosaic law in Reformed theology. A historical-redemptive approach is considered necessary for understanding Paul’s statements on the Mosaic Torah and covenant in Galatians 3–4, as well as in Reformed theology generally.