Beam tests of combinations of ATLAS calorimeters have been performed both for the barrel and end cap parts. During a combined test beam in summer 2004 a slice of the ATLAS barrel detector - including all detector sub systems from the inner tracker, the calorimetry to the muon system - was exposed to particle beams (electrons, pions, photons, muons) with different energies (1GeV to 350GeV). The aim was to study the combined performance of the different detector sub systems in ATLAS-like conditions. We will present the electronics calibration scheme of the electromagnetic calorimeter and its implementation. The following studies on the combined testbeam data have been performed and will be presented: performance of the electromagnetic calorimetry down to very low energies (> GeV), photon reconstruction including converted photons and position measurements using the very precise ATLAS tracker and the electromagnetic calorimeter. These measurements have been compared to Monte Carlo simulations showing the good description of the data. An end cap segment of the electromagnetic, hadronic and forward liquid argon calorimeters of ATLAS has been exposed to electron, pion and muon beams in the energy range from 10 to 200 GeV. The goal of this beamtest carried out at the CERN SPS is to obtain the calibration for the ATLAS calorimeter in a particular difficult transition region (2.4<3.8) between the various subdetectors, including the dead material effects. Results for electrons and pions will be presented and compared to MC simulation
