This paper reports progress in the development of a new Psychosocial Maturity Inventory. The subscales assess Self-reliance, Work Orientation, and Identity--theoretically, aspects of Individual Adequacy; Communication Skills, Knowledge of Major Roles, and Enlightened Trust--conceptualized as aspects of Interpersonal Adequacy; and Social Commitment, Tolerance, and Openness to Socio-political Change--viewed as aspects of Social Adequacy. Using a sample of 2,568 students divided among grades 5, 8, and 11, a single subscale of each trait was developed for use at all three grade levels. Kuder Richardson Formula 8 estimates of subscale homogeneity are presented, along with data demonstrating the relationship of each subscale to Social Desirability scores, to measures of three divergent traits, nd to chronological maturity (grade level). The validity of the conceptual model of psychosocial maturity, i.e., the arrangement of traits into three groups reflecting different types of adequacy, is tested empirically by (1) analysis of subscale intercorrelations, (2) hiearchical factor analysis of items, and (3) principal components analysis of subscale scores. (Author)