The ATLAS detector at LHC has been designed to cover a large physics program aiming at the understanding of the origin of the EW symmetry breaking. Muon signatures are one of the basic tools to trigger, select and measure final states relevant for tests of the Standard Model and searches for new physics. In this seminar the muon reconstruction in the ATLAS detector is described in details, giving emphasis to the complementarity of the inner tracking system and of the large muon spectrometer. The achieved muon signatures performance, as measured from collision data, is discussed together with the improvements expected from future studies based on larger samples and refined reconstruction strategies. The most recent results from two physics analyses that strongly rely on muon signatures, the search for heavy Z' bosons and for the SM Higgs decaying into four-leptons final states, are presented. Finally, prospects for SM Higgs searches with 2011 collected data and in the incoming data-taking period are given.