From the third year onwards the sexual life of children shows much in common with that of adults; it is differentiated from the latter, as we already know, by the absence of a stable organization under the primacy of the genital organs, by inevitable traits of a perverse order, and of course also by far less intensity in the whole impulse. But those phases of the sexual development, or as we will call it, of the _Libido-development_, which are of greatest interest theoretically lie before this period. This development is gone through so rapidly that direct observation alone would perhaps never have succeeded in determining its fleeting forms. Only by the help of psycho-analytic investigation of the neuroses has it become possible to penetrate so far back and to discover these still earlier phases of Libido-development. These phases are certainly only theoretic constructions, but in the practice of psycho-analysis you will find them necessary and valuable constructions. You will soon understand how it happens that a pathological condition enables us to discover phenomena which we should certainly overlook in normal conditions. Thus we can now define the forms taken by the sexual life of the child before the primacy of the genital zone is reached; this primacy is prepared for in the early infantile period, before the latent period, and is permanently organized from puberty onwards. In this early period a loose sort of organization exists which we shall call _pre-genital_; for during this phase it is not the genital component-instincts, but the _sadistic_ and _anal_, which are most prominent. The contrast between _masculine_ and _feminine_ plays no part as yet; instead of it there is the contrast between _active_ and _passive_, which may be described as the forerunner of the sexual polarity with which it also links up later. That which in this period seems masculine to us, regarded from the standpoint of the genital phase, proves to be the expression of an impulse to mastery, which easily passes over into cruelty. Impulses with a passive aim are connected with the erotogenic zone of the rectal orifice, at this period very important; the impulses of skoptophilia (gazing) and curiosity are powerfully active; the function of excreting urine is the only part actually taken by the genital organ in the sexual life. Objects are not wanting to the component-instincts in this period, but these objects are not necessarily all comprised in one object. The sadistic-anal organization is the stage immediately preceding the phase of primacy of the genital zone. Closer study reveals how much of it is retained intact in the later final structure, and what are the paths by which these component-instincts are forced into the service of the new _genital organization_. Behind the sadistic-anal phase of the Libido-development we obtain a glimpse of an even more primitive stage of development, in which the erotogenic mouth zone plays the chief part.