INVESTIGATIONS INTO THE NATURE AND DEVELOPMENT OF SOCIAL AND EMOTIONAL BEHAVIOR IN HUMAN INFANCY HAVE RAISED MANY RESEARCH ISSUES AND HAVE INDICATED MANY ADDITIONAL AREAS OF INQUIRY. EARLY AND CONTEMPORARY STUDIES HAVE BOTH BEEN CONCERNED WITH PROVIDING MORE PRECISE ANALYSES OF STIMULUS AND SITUATIONAL DETERMINANTS OF SOCIAL AND EMOTIONAL BEHAVIOR, ALTHOUGH THE EARLY STUDIES WERE PRIMARILY DESCRIPTIVE WHEREAS THE EMPHASIS TODAY IS ON ANALYTIC STUDIES. TWO IMPORTANT ASPECTS OF STIMULUS-AND-SITUATIONAL-DETERMINANTS RESEARCH ARE (1) THE DEVELOPMENT OF ATTACHMENT BEHAVIOR IN INFANTS (ESPECIALLY TO THE MOTHER) AND (2) THE ROLE OF VARIOUS STIMULUS CUES AS ELICITORS OR REINFORCERS OF BEHAVIOR. INVESTIGATIONS OF APPROACH AND WITHDRAWAL PROCESSES INVOLVE A SECOND MAJOR RESEARCH AREA. ASPECTS OF APPROACH AND WITHDRAWAL THAT DEAL ESSENTIALLY WITH THE DIRECTIONAL AND AROUSAL CHARACTERISTICS OF INFANT RESPONSES ARE (1) EXPLORATORY BEHAVIOR, (2) CURIOSITY, AND (3) INTRINSIC MOTIVATION. PRESENT RESEARCH PROBLEMS INVOLVE (1) ADEQUATE CONCEPTUALIZATION OF EMOTIONAL PROCESSES EARLY IN LIFE, (2) IDENTIFICATION OF THE BEHAVIORAL INDICATORS OF EMOTIONAL RESPONSES IN INFANTS, AND (3) DETERMINATION OF THE INFLUENCE OF OTHER BASIC PSYCHOLOGICAL PROCESSES ON SOCIAL AND EMOTIONAL BEHAVIOR. THIS PAPER WAS PRESENTED AT THE MERRILL-PALMER INSTITUTE CONFERENCE ON RESEARCH AND TEACHING OF INFANT DEVELOPMENT (FEBRUARY 9-11, 1967). IT IS TO BE PUBLISHED IN THE MERRILL-PALMER QUARTERLY, VOLUME 14, 1968. (WD)