This paper is a review of psychological studies on Identity and TAT (Thematic Apperception Test) and also examines the possibility of TAT for concepts of Identity, and from the viewpoint of "Individuation" and "Relatedness". The theory of Identity is constructed from the viewpoint of "Individuation" and "Relatedness". Especially, it is necessary to study Identity taking account of "Relatedness" with infants at an early stage. The TAT is recommended as an assessment to test for "Relatedness" at an early stage of development. The analysis of TAT is a recommended approach toward analyzing an interpersonal world. TAT seems to establish a theory of Identity from the viewpoint of "Individuation" and "Relatedness".