Three sections have been studied: the characteristics of the virus (to insist on in their genome, able to produce structural and regulating proteins), and mainly, their biological cycle that allows us to know where the different antiretroviral will act; the resistance phenomena produced by their high answered and mutant capacity; and on third place, it show up some results of the investigations carried out in the Hospital Universitario San Cecilio, Granada, on two aspects: realization and validation of algorithms of interpretation of mutation based on virologic answer, and comparison of the influence according to the adult or smaller number of mutations appeared with the resistances in front of active medicines.