The Marrow controversy (1718–22) most often is understood as a dispute between evangelical and legalistic parties within the eighteenth-century Kirk. Various forms of this analysis, however, leave certain questions unanswered. Rather than a clash between evangelicalism and legalism, the Marrow controversy was a collision between two differing developments of Scottish federal theology. Through the theological refinement precipitated by John Simson’s views, Thomas Boston and Ebenezer Erskine had crafted, from within the Scottish federal tradition, an evangelical federalism that emphasized the freeness and immediacy of grace. Through that same process of refinement, James Hadow had constructed, from within the same coherent Scottish federal tradition, an ordered federalism that emphasized the means through which God sovereignly bestowed his free grace upon sinners. These two federal systems, when confronted with the particular doctrinal expressions of The Marrow of Modern Divinity, produced both radically different readings of the same text and enduring controversy.