GENIE is a new neutrino event generator for the experimental neutrino physics community. Its goal is to develop a 'canonical' neutrino interaction physics Monte Carlo valid across all nuclear targets and neutrino flavors from MeV to PeV energy scales. The project focuses on the few-GeV energy range, the boundary between non-perturbative and perturbative regimes, relevant for current and near-future long-baseline neutrino experiments. GENIE is a large-scale C++ software system with over 120,000 lines of code, featuring a modern object-oriented design and extensive validation. The first official physics release was in August 2007, with the latest version being v2.4.4. It supports the full life-cycle of simulation and analysis tasks. GENIE addresses challenges in neutrino simulations, including the need for accurate modeling of interactions across a broad energy range. It incorporates nuclear physics models, cross section models, and hadronization models. The relativistic Fermi gas (RFG) nuclear model is used, with modifications for short-range nucleon-nucleon correlations. The cross section model calculates differential and total cross sections, essential for event generation. The hadronization model, AGKY, simulates hadronic showers, while the intranuclear rescattering model, INTRANUKE, handles reinteractions within the nucleus. GENIE's physics models include quasi-elastic scattering, elastic neutral current scattering, baryon resonance production, coherent neutrino-nucleus scattering, and non-resonance inelastic scattering. It also includes charm production and inverse muon decay models. The transition region between non-perturbative and perturbative regimes is handled with care to avoid theoretical inconsistencies and double-counting. The model is tuned using data from bubble chamber experiments and other sources, ensuring accuracy across a wide range of neutrino energies and targets. GENIE is used in experiments such as MINOS, T2K, and ArgoNEUT, and is a key tool for neutrino physics. It supports a wide range of simulation and analysis tasks, with a modular and extensible design. The collaboration includes physicists from major neutrino experiments, ensuring continued development and validation of the model. GENIE's design and implementation reflect the evolving needs of high-energy physics, providing a robust and flexible tool for neutrino interaction simulations.GENIE is a new neutrino event generator for the experimental neutrino physics community. Its goal is to develop a 'canonical' neutrino interaction physics Monte Carlo valid across all nuclear targets and neutrino flavors from MeV to PeV energy scales. The project focuses on the few-GeV energy range, the boundary between non-perturbative and perturbative regimes, relevant for current and near-future long-baseline neutrino experiments. GENIE is a large-scale C++ software system with over 120,000 lines of code, featuring a modern object-oriented design and extensive validation. The first official physics release was in August 2007, with the latest version being v2.4.4. It supports the full life-cycle of simulation and analysis tasks. GENIE addresses challenges in neutrino simulations, including the need for accurate modeling of interactions across a broad energy range. It incorporates nuclear physics models, cross section models, and hadronization models. The relativistic Fermi gas (RFG) nuclear model is used, with modifications for short-range nucleon-nucleon correlations. The cross section model calculates differential and total cross sections, essential for event generation. The hadronization model, AGKY, simulates hadronic showers, while the intranuclear rescattering model, INTRANUKE, handles reinteractions within the nucleus. GENIE's physics models include quasi-elastic scattering, elastic neutral current scattering, baryon resonance production, coherent neutrino-nucleus scattering, and non-resonance inelastic scattering. It also includes charm production and inverse muon decay models. The transition region between non-perturbative and perturbative regimes is handled with care to avoid theoretical inconsistencies and double-counting. The model is tuned using data from bubble chamber experiments and other sources, ensuring accuracy across a wide range of neutrino energies and targets. GENIE is used in experiments such as MINOS, T2K, and ArgoNEUT, and is a key tool for neutrino physics. It supports a wide range of simulation and analysis tasks, with a modular and extensible design. The collaboration includes physicists from major neutrino experiments, ensuring continued development and validation of the model. GENIE's design and implementation reflect the evolving needs of high-energy physics, providing a robust and flexible tool for neutrino interaction simulations.