In Germany, the final grade of a doctorate is significant for careers inside and outside the academic labor market. Particularly important is the highest grade--"summa cum laude." At the same time, doctoral grades are constantly subject to criticism. Thus far, however, neither German nor international studies have examined the determinants of doctoral grades. Drawing on Hu's model of college grades, this study develops a conceptual framework for explaining doctoral grades and investigates the impact of doctorate holders', reviewers', and environmental context characteristics on the probability of doctoral candidates graduating with the highest grade, "summa cum laude." Using logistic regression analyses on data from the German PhD Panel Study, the study confirms that high-performing individuals are more likely to achieve the highest doctoral grade. A learning environment that is characterized by supervision security, high expectations to participate in scientific discourse, and strong support in network integration also increases the chances of graduating with a "summa cum laude" degree. In contrast, being female, having a highly respected reviewer, studying natural sciences, medical studies or engineering, completing an external doctorate, and studying within a learning environment characterized by rigid time constraints are negatively related to the probability of receiving a "summa cum laude" grade. This study is the first to lend empirical evidence to the critical discussion of doctoral grades and offers insights to ensure the validity of doctoral grades.