This document reports on a search for the Standard Model Higgs boson in the diphoton decay channel in proton-proton collisions at center-of-mass energies of √s=7 TeV and √s= 8 TeV using integrated luminosities of 4.8 fb−1 and 5.9 fb−1, respectively, recorded with the ATLAS detector at the Large Hadron Collider. The search is performed for Higgs boson masses between 110 and 150 GeV. The expected exclusion limit at 95% confidence level varies between 0.8 and 1.6 times the StandardModel cross section over the studied mass range, and results in an expected exclusion range from 110 GeV to 139.5 GeV. The observed exclusion ranges for a Standard Model Higgs boson are found to be (112-122.5) GeV and (132-143) GeV at 126.5 GeV with a local significance of 4.5 σ. An excess is observed at 126.5 GeV with a signal strength of 1.8 over the SM expectation.