The topic of justification stands as a kind of forbidden forest in Pauline Studies—a sinister and menacing realm patrolled by outsized, territorial creatures known to engage each other in fearsome combat. In this book, James Prothro makes a bold entrance into the forest, showing himself to be not only courageous but capable of holding his own. The charm of Prothro’s project lies in its modesty: he restricts his focus to Paul’s handling of the verb δικαιόω and seeks to explain, specifically, what God effects through the activity of “justifying.” Prothro advances the thesis that δικαιόω derives from and extends a Greco-Jewish register. The Septuagint, he argues, is the lexicon needed to gloss Paul’s use of the term, and he concludes that when it appears as a designation for divine action, “to justify” names a favorable verdict rendered by God. God is the one who judges and the one who justifies, as the book’s title declares.The nature of Prothro’s thesis demands that he attend both to the Septuagint, Paul’s sourcebook, as well as to Paul’s writings themselves. Chapters 2–4 address the first component. Prothro’s analysis finds that authors employ “justifying” language in two kinds of legal scenarios, which he labels “bilateral contentions” and “trilateral contentions.” The former refers to disputes between two parties in which no authoritative intermediary is present; the latter includes such an intermediary, who steps in to adjudicate between two parties, ultimately finding one of those parties to be “in the right.” When God features as an actor in these contentions—whether as accuser or accused (= bilateral) or as judge (= trilateral)—his testimony is unassailable and his judgment the one that counts. When God “justifies,” more narrowly, he does so “precisely [to] those against whom he has a legitimate claim” (p. 208), or in vindication of one party against another.Chapters 5–8 address Paul’s writings, the second component, and consider 1 Corinthians, Galatians, and Romans. In 1 Corinthians, Paul twice uses δικαιόω as a predicate for divine action (1 Cor 4:4, 6:11). Prothro classifies both as bilateral contentions, maintaining that, while the timing of God’s “justifying” activity is notably different, the kind of action connoted remains constant: God determines the offending humans to be in the right. In Galatians, Paul frequently utilizes δικαιόω (Gal 2:16–17; 3:8, 11, 24; 5:4) and infamously abstains from defining it. Prothro insists that Paul’s letter presupposes a theological foundation already laid for his original readers. Approaching Galatians with this acknowledgement, we can discern that Paul draws on the bilateral contention framework and includes “justifying” language to bespeak God’s “finding in favor” of humans in spite of genuine culpability. In Romans, Paul deploys δικαιόω in dense concentration, predominantly in contexts that again depict the bilateral framework. On one occasion, though, Prothro thinks Paul’s use of δικαιόω reflects a trilateral contention. According to him, the enigmatic expression ὁ . . . ἀποθανὼν δεδικαίωται ἀπὸ τῆς ἁμαρτίας (Rom 6:7) evokes a scene in which God vindicates Jesus (that is, “the One who died”) in the face of Sin by means of raising Jesus from the dead. Although the setting here changes, the verb’s foundational concept holds: God “finds in favor” of the Messiah.Where, then, does this illuminating study of “justifying” language ultimately lead? Prothro memorably declares, “There are a number of ways in which Paul’s expression of the gospel is innovative and polemical within Judaism and early Christianity. His theological-legal use(s) of δικαιόω is not one of them” (p. 210). The limited scope of the project will prove underwhelming to some (as Prothro himself concedes), and others will question the prudence of siloing a term in the way he elected to do it. However, the points of contact that he identifies between Paul and Paul’s Jewish forebearers mandate careful appraisal. Thus, while not everyone will concur with the thesis, no one can summarily dismiss it.