Geant4 is a software toolkit for simulating the passage of particles through matter, used in various fields including high energy physics, astrophysics, medical physics, and radiation protection. It provides comprehensive detector and physics modeling capabilities, with continuous improvements in functionality and performance. Recent developments include performance optimization for complex setups, improvements in field propagation, event biasing options, and enhancements in geometry, physics processes, and interactive capabilities. The toolkit uses object-oriented technology and follows an iterative software process, allowing for easy extension and refinement without affecting production code. New developments in the Geant4 kernel include improvements in run and event management, region-dependent production thresholds, and variance reduction techniques. The Run Manager module has been redesigned to allow more flexible and customizable run management, while region-dependent production thresholds enable different particle production thresholds in different regions of the setup. Variance reduction techniques, such as importance biasing, have been introduced to improve simulation efficiency. Improvements in detector modeling include new geometry features, such as the G4TwistedTubs and G4TwistedTrap solids, which allow for more accurate modeling of complex detector components. The toolkit also supports the visualization of detector geometry and particle trajectories, with various tools for viewing and analyzing simulation data. Physics extensions include improvements in electromagnetic and hadronic processes, with new models and validation against experimental data. The toolkit has been validated against authoritative reference data, including the National Institute of Standards and Technology (NIST) database, ensuring accuracy in simulations. Geant4 is used in a wide range of experimental applications, including particle detectors, space telescopes, dark matter searches, and medical physics. It supports parallel processing for large-scale simulations and is used in production by large high energy physics experiments and smaller detector development projects. The toolkit continues to be developed and validated to meet the evolving needs of the experimental community.Geant4 is a software toolkit for simulating the passage of particles through matter, used in various fields including high energy physics, astrophysics, medical physics, and radiation protection. It provides comprehensive detector and physics modeling capabilities, with continuous improvements in functionality and performance. Recent developments include performance optimization for complex setups, improvements in field propagation, event biasing options, and enhancements in geometry, physics processes, and interactive capabilities. The toolkit uses object-oriented technology and follows an iterative software process, allowing for easy extension and refinement without affecting production code. New developments in the Geant4 kernel include improvements in run and event management, region-dependent production thresholds, and variance reduction techniques. The Run Manager module has been redesigned to allow more flexible and customizable run management, while region-dependent production thresholds enable different particle production thresholds in different regions of the setup. Variance reduction techniques, such as importance biasing, have been introduced to improve simulation efficiency. Improvements in detector modeling include new geometry features, such as the G4TwistedTubs and G4TwistedTrap solids, which allow for more accurate modeling of complex detector components. The toolkit also supports the visualization of detector geometry and particle trajectories, with various tools for viewing and analyzing simulation data. Physics extensions include improvements in electromagnetic and hadronic processes, with new models and validation against experimental data. The toolkit has been validated against authoritative reference data, including the National Institute of Standards and Technology (NIST) database, ensuring accuracy in simulations. Geant4 is used in a wide range of experimental applications, including particle detectors, space telescopes, dark matter searches, and medical physics. It supports parallel processing for large-scale simulations and is used in production by large high energy physics experiments and smaller detector development projects. The toolkit continues to be developed and validated to meet the evolving needs of the experimental community.