Relational reasoning is the foundational cognitive ability to discern meaningful patterns within an informational stream, but its reliable and valid measurement remains problematic. In this investigation, the measurement of relational reasoning unfolded in three stages. Stage 1 entailed the establishment of a research-based conceptualization of the construct and the development of a corresponding Test of Relational Reasoning (TORR). Stage 2 focused on the reliability and validity of data from the TORR. Analyses showed the data from the TORR to be reliable indicators of students' ability to reason relationally, and TORR performance predicted students' performance on SAT verbal and math problems. Stage 3 examined the underlying structure of the construct through Confirmatory Factor Analysis (CFA). Of the three CFA models tested, models with dedicated factors for analogical, anomalous, antinomous, and antithetical reasoning were deemed the best fit for the data.