This study analyzes the contributions of Sigmund Freud, Sándor Ferenczi and Jacques Lacan to the concept of trauma in Psychoanalysis, highlighting the main theoretical frameworks in each approach. The concept of trauma has undergone different changes in the various phases of the theoretical Freudian conception, and its diverse meanings have been discussed since the first seduction theory up to the latest theory of anguish (Freud, 1926 [1925]), as well as in Moses and the monotheism (Freud, 1939 [1934-1938]). In Ferenczi, there are two approaches: in the first one, the traumas are of a structuring nature, which means they are either needed, inevitable or philogenetic; in the second one the traumatic situations put the identification project of the subject at risk. In that last approach, the trauma depends on a failure of the relation between the subject and the other. By valuing the alterity in the constitution of trauma, Ferenczi is faithful to what his clinics has revealed: trauma is basically the result of an action of the other upon the one who has been traumatised. In Lacan, on the other hand, the trauma is understood as the entry of the subject into the symbolic world; it is not an accident in the speaking person s life, but rather it is constitutive of their identity. Therefore, trauma in the present study is examined at the light of the relationship established by Lacan between the notions of trauma and signifier, and it also is permeated by the idea of trauma as an encounter with the Real.