The knowledge of life's cycle of the acquired immune deficiency syndrome's virus (HIV) its complex genetic structure involving the interaction of positive and negative regulatory gene controlling the growth of the virus, its great genetic variability, the different pathogenic mechanisms, the cell-virus interaction, the different host-cells and the interaction of other pathogens, are all fundamentals facts for a better understanding of the various stages of infection by HIV until ultimate establishment of the Acquired Immune Deficiency Syndrome and also to explain the therapeutic difficulties until now.