This article is a theological contribution to the debate over the contested Pauline expression πίστις Ἰησοῦ Χριστοῦ. I begin by assessing Karl Barth's christological conception of faith in his Church Dogmatics, focusing on the themes of history, obedience, and imitation. Except for a significant passage in CD 2/2, Barth consistently employs the objective genitive, but his christocentric pisteology enables it to do the same work accomplished by the subjective genitive argued for by Richard Hays. Barth, however, does not connect his trinitarian theology to the text of Galatians, and Hays does not give sufficient attention to the life of Christ or to the agency of the Spirit. In the bulk of the paper, therefore, I explore the missional-trinitarian shape of faith through a theological exegesis of Galatians in order to supplement the insights of Barth and Hays. I argue that Paul presents a missional narrative in which Father, Son, and Spirit are each involved in actualizing the faith of the community. We can thus speak of the faithfulness of the Father, the faith of the Son, and the faith-producing Holy Spirit. A trinitarian interpretation of Galatians is able to ground the distinction between the objective and subjective dimensions of faith in the mission of the triune God.