Yves Congar's and Hans Küng's modes of participation at Vatican II reflect different visions of ecclesial reform. Congar followed an 'inside' path, working on the conciliar commissions that produced Vatican II's documents; Küng chose an 'outside' path, pursuing his own writing projects and engaging the mass-media. Their choice of differing paths was neither arbitrary nor merely temperamental, but cohered in both instances with substantial theologies of reform. Attending to the inseparability of the historical-biographical and systematic dimensions of their respective trajectories, this article first examines Congar's evaluation of his own role at the Council and of the roles of other participants, as witnessed by his conciliar journal spanning the years 1960 to 1966. The article then does likewise for Küng, drawing primarily upon his memoirs. It concludes by comparing their paths of reform and addressing the implications of their differences. Yves Congar's and Hans Küng's modes of participation at Vatican II reflect different visions of ecclesial reform. Congar followed an 'inside' path, working on the conciliar commissions that produced Vatican II's documents; Küng chose an 'outside' path, pursuing his own writing projects and engaging the mass-media. Their choice of differing paths was neither arbitrary nor merely temperamental, but cohered in both instances with substantial theologies of reform. Attending to the inseparability of the historical-biographical and systematic dimensions of their respective trajectories, this article first examines Congar's evaluation of his own role at the Council and of the roles of other participants, as witnessed by his conciliar journal spanning the years 1960 to 1966. The article then does likewise for Küng, drawing primarily upon his memoirs. It concludes by comparing their paths of reform and addressing the implications of their differences.