As a field, educational measurement has strong and essential ties to educational psychology. Practitioners in educational measurement, almost by definition, are closely linked to educational psychology for the basis of their theoretical and pedagogical principles. Researchers in educational measurement are often dependent on educational psychologists for the theoretical underpinning of the psychometric principles and applications they pursue in their scholarly endeavors. Reciprocally, educational psychologists rely on educational measurement for providing the essential psychometric tools for analyzing and applying their educational psychology theories and practices. The details of this close and necessary linkage between educational psychology and educational measurements will be addressed further in this chapter, which will focus on how this interrelationship may evolve and expand in the future.