The system of Moreno's sociometry has been disjointed with times against the will of Moreno. One can find some justifiable reasons for it. The development and differentiation of sociometry can be reviewed at least from two points of view; the chronological development and the development of each branch within the sociometric system. The former is discussed in the present paper. The development of sociometry is chronologically divided into three parts as follows. (1) Hot sociometry period (1923-1937): The practical aspect of sociometry was emphasized more that the theoritical one during this period. Research was only a by-product in the process of therapy. the goal of sociometric study was to change the conflicting society and group into healthy ones with sociometric procedures. (2) Cold sociometry period (1937-1950): The sociometry of this period aimed at describing, measuring and estimating the group structure and interpersonal relationship within it and refining sociometric techniques. Emphasis had shipted from therapy to diagnosis. the system of Moreno's sociometry was differentiated with this shift and each branch within the system developed separately. (3) Perceptual sociometry period (1950- ) Introversion of sociometric test, that is, awareness of other person's choice is the major subject at present. The psychological dynamics of choice behavior is being definitely shown by the researches of these kinds.