The paper presents the concept of personality as formulated by J.P.Sartre based on his work Being and Nothingness (Gallimard, Paris 1943). The characteristic point of Sartre's theory of personality is accepting as elements of the structure of personality the internal processes (a project to be) and defining personality as non-natural but a creative system composed of functional structure. The background of Sartre's theory is the concept of becoming, understood widely as an intentional action of the subject in the world he perceives and comprehends. It is additionally accompanied by a specific concept of identity. Identity is understood as relation required for the most favourable functioning of the subject. The personality of the subject and all motivational processes to become a personality, occur within the basic psychological unit: Individual-World. Sartre detailed on his work Being and Nothingness how the construction of the own personality is part of the project to be of human reality, fleeing from finitude and its ground, in a situation it never chose. Sartre described also how faced, with this finite freedom, the human personality for the most part is the choice of avoiding its genuine choices in order to vainly attempt to achieve a Godlike freedom that would first choose its situation and then choose again, on the basis of being its own source of foundation. He argued also that the personality is a spontaneous upsurge into the world. Sartre's conception of personality is an example of a holistic approach. It constitutes a theoretical draft with elements of systematic theory. The method of investigation used by Sartre is a phenomenological analysis of the various possible presentations of the phenomenon under study, varying in free play, has been repeatedly overlooked and misunderstood. It seems that this analysis (used already by Husserl) has a potential heuristic power and discovers the essence of personality very well. The text also discusses fundamental question about psychotherapeutic help. Sartre confirmed that nobody can help anyone without accepting human freedom. Everybody is able to accept or to reject this freedom. For Sartre, however, human freedom is a total responsibility and an ungrounded upsurge, inseparable from the totality, its situation, its context. For Sartre, the flight from the situatedness of human existence, attempted through belief in an empirical personality (ego) as an absolute foundation is only reinforced by the philosopher's theorizing of a transcendental ego as the agent of consciousness. Only liberty can be an absolute foundation of the human personality or human ego and every psychotherapy has to help men to understand this.