Although the covenant was a relatively known theme among sixteenth-century early Reformers, Bullinger’s theology —as reflected in his treatise A Brief Exposition of the One and Eternal Testament or Covenant of God (hereafter Covenant of God) — develops further Zwingli’s notion of the covenant. Although we can’t say that the covenant is a central hermeneutical principle to understand all Bullinger’s theology, his development of the covenant offers some good insights. Testamentum as Covenant Due to the diversity of meanings, Bullinger starts clarifying his understanding of the term ‘testamentum.’ He understands ‘testamentum’ as an oath-based promise taking into account what Scripture …