THE PROCESSES OF THOUGHT, OF CONCEPT DEVELOPMENT, AND OF VOCABULARY DEVELOPMENT ARE SIGNIFICANTLY INTERRELATED. COMMUNICATION OF IDEAS DEPENDS UPON THE ABILITY TO ASSOCIATE WRITTEN AND VERBAL SYMBOLS WITH THE REFERENTS THROUGH A SYSTEMATIC PROCESS OF REORGANIZING AND INTEGRATING OLD AND NEW CONCEPTS. THE ABILITY TO ASSOCIATE, IN TURN, DEPENDS UPON VOCABULARY DEVELOPMENT. HENCE, A WELL-DEVELOPED STRUCTURE OF CONCEPT ASSOCIATIONS IS A FUNCTION OF VOCABULARY-CONCEPT RELATIONSHIPS. CONCEPTS ARE GENERAL IDEAS WHICH INVOLVE DISCRIMINATION AND GENERALIZATION. THEY EXIST AT ALL LEVELS OF COMPLEXITY, DEVELOP GRADUALLY FROM SIMPLE TO COMPLEX MENTAL CONSTRUCTS, AND MUST BE SYMBOLIZED TO BE COMMUNICATED EFFECTIVELY. WHILE AUTHORITIES IN THE FIELD ARE AWARE OF THE DIFFICULTY OF IDENTIFYING, ISOLATING, STUDYING, AND EVALUATING CONCEPTS, THEY RECOGNIZE THEIR IMPORTANCE TO THE ACQUISITION OF KNOWLEDGE AND TO SUCCESS IN READING. SIGNIFICANT STUDIES ON CONCEPT DEVELOPMENT CITED ARE THOSE OF PIAGET, RUSSELL, BRAUN, AND DOWNEY. THIS ARTICLE APPEARED IN "JOURNAL OF READING," VOLUME 10, APRIL 1967. (NS)