We discuss Klein's, Winnicott's, and Mahler's object relational theories relevant for creating and maintaining the mature love relationship. The concept of love refers to the basic human relationship. The capacity for adult love involves the attainment of the relation towards the object as whole, satisfying the emotional needs of the self, including simultaneous tolerance of the specific needs of the object. It also involves the optimum resolution of anxiety related to schizo-paranoid and depressive positions and phases of separation and individuation. Primitive defense mechanisms, such as splitting, are replaced by more mature defense mechanisms, and primitive idealization is replaced by more mature idealization. The fusion with the object is reversible and helps in creating the experience of closeness with the partner, while the possibility of separation provides the possibility of recognizing and respecting the differences. Obstacles in the development of object relationships from pre-object to object phase, from symbiotic to separation and individuation phase can impair the capacity to love.