The LHCb detector, located at the Large Hadron Collider (LHC) at CERN, is designed for precision measurements of CP violation and rare decays of beauty and charm hadrons. This paper evaluates the performance of the various sub-detectors and the trigger system using data from 2010 to 2012, demonstrating that the experiment meets its design criteria. The excellent performance of the detector has enabled the LHCb collaboration to publish a wide range of physics results, highlighting its unique role as both a heavy flavor experiment and a general-purpose detector in the forward region. The paper covers several key aspects of the LHCb detector, including charged particle reconstruction, neutral particle reconstruction, particle identification, and trigger performance. It discusses the tracking system, which consists of the VELO, Tracker Turicensis (TT), Inner Tracker (IT), and Outer Tracker (OT), and their contributions to vertexing, momentum measurement, and particle identification. The calorimeter system, including the SPD, PS, ECAL, and HCAL, is described, along with its role in identifying particles and measuring their energies. The muon detection system, which provides muon identification and contributes to the L0 trigger, is also detailed. The paper then delves into the performance of the trigger system, which consists of two levels: the Level-0 hardware trigger and the High Level Trigger (HLT). The Level-0 trigger reduces the event rate from 40 MHz to 1.1 MHz, while the HLT processes the remaining events using a simplified offline event reconstruction. The paper also discusses the data-taking periods and operating conditions, including the evolution of luminosity and pile-up, and the impact of these factors on the detector performance. Overall, the paper provides a comprehensive overview of the LHCb detector's performance, highlighting its capabilities in precision measurements and its significant contributions to the field of flavor physics.The LHCb detector, located at the Large Hadron Collider (LHC) at CERN, is designed for precision measurements of CP violation and rare decays of beauty and charm hadrons. This paper evaluates the performance of the various sub-detectors and the trigger system using data from 2010 to 2012, demonstrating that the experiment meets its design criteria. The excellent performance of the detector has enabled the LHCb collaboration to publish a wide range of physics results, highlighting its unique role as both a heavy flavor experiment and a general-purpose detector in the forward region. The paper covers several key aspects of the LHCb detector, including charged particle reconstruction, neutral particle reconstruction, particle identification, and trigger performance. It discusses the tracking system, which consists of the VELO, Tracker Turicensis (TT), Inner Tracker (IT), and Outer Tracker (OT), and their contributions to vertexing, momentum measurement, and particle identification. The calorimeter system, including the SPD, PS, ECAL, and HCAL, is described, along with its role in identifying particles and measuring their energies. The muon detection system, which provides muon identification and contributes to the L0 trigger, is also detailed. The paper then delves into the performance of the trigger system, which consists of two levels: the Level-0 hardware trigger and the High Level Trigger (HLT). The Level-0 trigger reduces the event rate from 40 MHz to 1.1 MHz, while the HLT processes the remaining events using a simplified offline event reconstruction. The paper also discusses the data-taking periods and operating conditions, including the evolution of luminosity and pile-up, and the impact of these factors on the detector performance. Overall, the paper provides a comprehensive overview of the LHCb detector's performance, highlighting its capabilities in precision measurements and its significant contributions to the field of flavor physics.