AMS is a general purpose spectrometer to measure cosmic rays and cosmic photons in near Earth orbit. I review selected results from the AMS-01 pilot experiment on board space shuttle mission STS-91, concerning the observation of cosmic protons and helium and the search for cosmic antimatter. I then introduce the more ambitious AMS-02 detector scheduled for installation on the International Space Station in 2005. Its expected performance in the search for antimatter and dark matter, in research on the origins and propagation of cosmic rays as well as on high energy photon sources is presented. Possible extensions to higher energies are also discussed.