The goal of antiretroviral therapy is to interrupt the disease progression and to approach normal life expectancy for individuals with HIV. The condition for this is to deter the emergence of resistant HIV. This aim is achieved by improved patient drug adherence, sufficient enteral resorption and the control of interactions, as well as good tolerability and full antiviral activity. An insufficient drug exposure for protease inhibitors is overcome by the use of a booster agent. Emerging HIV-resistance can be described in a phase model:Phase 1:replication of wild-type HIV under incomplete suppressive therapy. Phase 2:transformation of wild-type into resistant HIV through accumulation of mutations. A preventive, resistance-guided switch of therapy preserves therapeutic options for the future. Phase 3:replication of resistant HIV (no more mutations possible).a)stable immunity: continue with failing therapy.b)threatening disease progression: resistance-guided switch to a salvage-regimen.