This paper provides a comprehensive overview of the ATLAS experiment, installed at the Large Hadron Collider (LHC) at CERN. It describes the detector's design, components, and expected performance. The ATLAS detector is a general-purpose experiment designed to study proton-proton and nucleus-nucleus collisions at high energies. Key components include the inner detector, electromagnetic and hadronic calorimeters, muon spectrometer, forward detectors, and trigger and data acquisition systems. The inner detector, immersed in a 2 T magnetic field, uses semiconductor pixel and strip detectors for precise tracking. The electromagnetic calorimeter, with excellent energy and position resolution, covers the pseudorapidity range $|\eta| < 3.2$. The hadronic calorimeters, using scintillator-tile technology, cover $|\eta| < 1.7$ and end-caps. The muon spectrometer, surrounded by the calorimeters, provides high-precision tracking and muon identification. Forward detectors, including LUCID, ALFA, and ZDC, measure luminosity and centrality in heavy-ion collisions. The trigger system, with three levels (L1, L2, and event filter), reduces the data rate from 1 GHz to 200 Hz. The paper also discusses radiation levels, shielding, and the interface with the LHC machine, emphasizing the challenges posed by high interaction rates and radiation doses.This paper provides a comprehensive overview of the ATLAS experiment, installed at the Large Hadron Collider (LHC) at CERN. It describes the detector's design, components, and expected performance. The ATLAS detector is a general-purpose experiment designed to study proton-proton and nucleus-nucleus collisions at high energies. Key components include the inner detector, electromagnetic and hadronic calorimeters, muon spectrometer, forward detectors, and trigger and data acquisition systems. The inner detector, immersed in a 2 T magnetic field, uses semiconductor pixel and strip detectors for precise tracking. The electromagnetic calorimeter, with excellent energy and position resolution, covers the pseudorapidity range $|\eta| < 3.2$. The hadronic calorimeters, using scintillator-tile technology, cover $|\eta| < 1.7$ and end-caps. The muon spectrometer, surrounded by the calorimeters, provides high-precision tracking and muon identification. Forward detectors, including LUCID, ALFA, and ZDC, measure luminosity and centrality in heavy-ion collisions. The trigger system, with three levels (L1, L2, and event filter), reduces the data rate from 1 GHz to 200 Hz. The paper also discusses radiation levels, shielding, and the interface with the LHC machine, emphasizing the challenges posed by high interaction rates and radiation doses.