The CMS detector, designed for particle-flow (PF) reconstruction, features a highly-segmented tracker, a fine-grained electromagnetic calorimeter (ECAL), a hermetic hadron calorimeter (HCAL), a strong magnetic field, and an excellent muon spectrometer. A fully developed PF reconstruction algorithm was implemented, enabling the identification and reconstruction of all final-state particles in each collision. This approach provides a global event description, improving the performance of jet and hadronic τ decay reconstruction, missing transverse momentum determination, and electron and muon identification. It also allows for efficient pileup mitigation by identifying particles from pileup interactions. Data collected at 8 TeV show excellent agreement with simulations, confirming the superior PF performance up to an average of 20 pileup interactions. The CMS detector is well-suited for PF reconstruction due to its large magnetic field, fine-grained tracker, highly-segmented ECAL, hermetic HCAL, and excellent muon tracking system. The magnet provides a uniform field of 3.8 T, aiding in separating charged and neutral particle energy deposits. The silicon inner tracker, with a fine granularity, allows for precise trajectory reconstruction. The ECAL, made of PbWO₄ crystals, provides excellent energy resolution and photon identification. The HCAL, with a sampling structure, allows for accurate hadron energy measurement. The muon detectors provide efficient and pure muon identification. The PF reconstruction algorithm links basic elements from all detector layers to identify each final-state particle, combining measurements to reconstruct particle properties. This holistic approach improves the efficiency and resolution of physics objects. The algorithm was implemented in 2010 and has been used in all CMS physics analyses. The performance of the resulting physics objects was compared to traditional methods, showing superior results. The algorithm also mitigates pileup effects by identifying and masking detector backgrounds. The CMS detector's properties, including the magnet, silicon inner tracker, ECAL, HCAL, and muon detectors, are described in detail. The ECAL and HCAL have high energy resolution and granularity, allowing for accurate energy measurement. The muon detectors provide efficient and pure muon identification. The PF reconstruction algorithm was tested and validated with Monte Carlo simulations and real data, demonstrating its effectiveness in identifying particles and mitigating pileup effects. The algorithm is now a standard for CMS physics analyses and is used in future detector designs.The CMS detector, designed for particle-flow (PF) reconstruction, features a highly-segmented tracker, a fine-grained electromagnetic calorimeter (ECAL), a hermetic hadron calorimeter (HCAL), a strong magnetic field, and an excellent muon spectrometer. A fully developed PF reconstruction algorithm was implemented, enabling the identification and reconstruction of all final-state particles in each collision. This approach provides a global event description, improving the performance of jet and hadronic τ decay reconstruction, missing transverse momentum determination, and electron and muon identification. It also allows for efficient pileup mitigation by identifying particles from pileup interactions. Data collected at 8 TeV show excellent agreement with simulations, confirming the superior PF performance up to an average of 20 pileup interactions. The CMS detector is well-suited for PF reconstruction due to its large magnetic field, fine-grained tracker, highly-segmented ECAL, hermetic HCAL, and excellent muon tracking system. The magnet provides a uniform field of 3.8 T, aiding in separating charged and neutral particle energy deposits. The silicon inner tracker, with a fine granularity, allows for precise trajectory reconstruction. The ECAL, made of PbWO₄ crystals, provides excellent energy resolution and photon identification. The HCAL, with a sampling structure, allows for accurate hadron energy measurement. The muon detectors provide efficient and pure muon identification. The PF reconstruction algorithm links basic elements from all detector layers to identify each final-state particle, combining measurements to reconstruct particle properties. This holistic approach improves the efficiency and resolution of physics objects. The algorithm was implemented in 2010 and has been used in all CMS physics analyses. The performance of the resulting physics objects was compared to traditional methods, showing superior results. The algorithm also mitigates pileup effects by identifying and masking detector backgrounds. The CMS detector's properties, including the magnet, silicon inner tracker, ECAL, HCAL, and muon detectors, are described in detail. The ECAL and HCAL have high energy resolution and granularity, allowing for accurate energy measurement. The muon detectors provide efficient and pure muon identification. The PF reconstruction algorithm was tested and validated with Monte Carlo simulations and real data, demonstrating its effectiveness in identifying particles and mitigating pileup effects. The algorithm is now a standard for CMS physics analyses and is used in future detector designs.