The author studies the mechanisms concerned to the human grouping and their uses for therapeutic purposes, stressing that the phenomenon of interaction is the basic dynamism in the group reactions. Parallels are traced between the author's ideas and Bion's point of view; a comparative study is also made of Moreno, Bion and Sullivan's ideas. The author suggests that the feelings of love and hostility appear in connection with the good or bad functioning of the primary contact, which characterizes the dependence. The author comments the results obtained with the use of a psychodrama which allowed the study of emotional reactions of envy, hate, aggression and love. An attempt is made to understand Slavson's and Pratt's techniques. Beukemkamp's study is mentioned as an original contribution to the understanding of the transferential phenomenon. Differences between the group and the individual therapeutics are pointed. Counter-transference is considered as a constructive element. The dramatic feeling experienced by the group or by one of its members is important because it involves verbalization, emotional components and bodily expression. The emotional level experienced by the group is more intense and oppressive than the ones experienced individually, and for justification of it the author mentions the circular reaction. The author thinks that Group Psychotherapy and Individual Psychotherapy are not opposing methods, but that they complement each other.