Part I. Evolution of the Goodness of Fit Concept. Goodness of Fit: A Special Development Concept and its Clinical Application. The Origins of the Goodness of Fit Concept. Critique of other Major Developmental Concepts and Clinical Applications. Review of the Literature: Clarification and Evolution of the Goodness of Fit Concept. Part II. Goodness of Fit: Clinical Applications. Infancy. Toddler and Preschool Periods. School Age and Middle Childhood. Adolescence. Adulthood. Personality Development: Continuity and Change. Part III. The Importance of the Biopsychosocial Model. Intertwining Goodness of Fit and the Biopsychosocial Model. Ethnic-Social Issues. Educational Issues. Sexual Issues. Marital Problems. Physical and Mental Handicaps. Part IV. Clinical Application. Prevention and Early Intervention of Childhood Behavior Problems. Poorness of Fit: Normalcy and Vulnerability vs. Pathology. Part V. Conclusion: Basic Structure of Goodness of Fit. The Clinician's Guidelines for the Applications of the Goodness of Fit Concept. Overview and a Look to the Future. Appendix A: Temperament Definitions, Categories, and Ratings. Bibliography.