This article aims to enhance understanding of the nomological network of expectancy of success beliefs related to mathematics. To this end, the paper uses the expectancy-value, regulatory focus, and regulatory mode theoretical frameworks and investigates 3 key classes of motivation predictors: (a) General motivation predispositions that center on students’ ideal (vs. ought) self-conceptualizations and contribute to the development of their self-schemas (i.e., promotion, prevention, locomotion, and assessment); (b) School-related achievement motives (i.e., need for achievement and fear of failure); and (c) Domain-specific autonomous and controlled reasons undergirding motivation to study mathematics. To examine the relationships between these antecedents and expectancies of success, data were collected from a sample of 5732 students enrolled in years 10 through 13 in 1 of 19 secondary schools. The results of exploratory structural equation modeling analyses indicated that studying to fulfill one’s aspirations and having a promotion focus were generally the strongest predictors of expectancies of success. In contrast, the other motivation predispositions, school-related achievement motives, and controlled reasons for studying mathematics had weaker or nonsignificant relationships with the criterion. Across the total sample as well as the subgroups investigated (i.e., school year and gender), the model accounted for substantial variability in students’ expectancies of success in mathematics. These findings have important implications for advancing understanding of the motivation beliefs of secondary school students.