The ReaxFF reactive force-field is a computational tool for exploring, developing, and optimizing material properties. It bridges the gap between quantum mechanics (QM) and empirical interatomic potentials, offering a balance between accuracy and computational efficiency. Unlike QM methods, which are computationally expensive, ReaxFF uses a bond-order formalism to implicitly describe chemical bonding without requiring expensive QM calculations. This allows simulations to model dynamic processes over longer timeframes and on larger scales, making it suitable for reactive events. ReaxFF has been developed and applied to various systems, including heterogeneous catalysis, atomic layer deposition (ALD), and reactive processes at interfaces between gas, liquid, and solid phases. It enables the simulation of complex processes involving multiple phases in contact, such as the growth of carbon nanotubes (CNTs) on nickel surfaces, the reduction of graphene oxide, and the oxidation of metal surfaces. ReaxFF has also been used to study the behavior of materials in aqueous environments, including the interaction of glycine with titanium dioxide surfaces and the conformational dynamics of biomolecules in solution. Recent developments in ReaxFF include the introduction of new simulation techniques such as Grand Canonical Monte Carlo/Molecular Dynamics (GC-MC/MD), Uniform-acceptance force-biased Monte Carlo (UFMC), Parallel Replica Dynamics (PRD), and Adaptive Accelerated ReaxFF Reaction Dynamics (aARRDyn). These methods enhance the ability to simulate rare events and kinetic processes that are otherwise inaccessible to traditional molecular dynamics (MD) simulations. Additionally, improvements in charge description, such as the incorporation of ACKS2, have enhanced the accuracy of ReaxFF in describing electronic interactions and physisorption processes. Future developments of ReaxFF aim to improve its ability to model interfacial chemistry in batteries and structural/polarization behavior in piezoelectric and ferroelectric materials. The introduction of explicit electron description (eReaxFF) allows for more accurate simulations of electron affinity in radical species, providing a significant improvement over standard ReaxFF. Ongoing efforts focus on optimizing ReaxFF parameters and expanding its applications to modern architectures, making it more accessible and efficient for a wide range of scientific and engineering applications.The ReaxFF reactive force-field is a computational tool for exploring, developing, and optimizing material properties. It bridges the gap between quantum mechanics (QM) and empirical interatomic potentials, offering a balance between accuracy and computational efficiency. Unlike QM methods, which are computationally expensive, ReaxFF uses a bond-order formalism to implicitly describe chemical bonding without requiring expensive QM calculations. This allows simulations to model dynamic processes over longer timeframes and on larger scales, making it suitable for reactive events. ReaxFF has been developed and applied to various systems, including heterogeneous catalysis, atomic layer deposition (ALD), and reactive processes at interfaces between gas, liquid, and solid phases. It enables the simulation of complex processes involving multiple phases in contact, such as the growth of carbon nanotubes (CNTs) on nickel surfaces, the reduction of graphene oxide, and the oxidation of metal surfaces. ReaxFF has also been used to study the behavior of materials in aqueous environments, including the interaction of glycine with titanium dioxide surfaces and the conformational dynamics of biomolecules in solution. Recent developments in ReaxFF include the introduction of new simulation techniques such as Grand Canonical Monte Carlo/Molecular Dynamics (GC-MC/MD), Uniform-acceptance force-biased Monte Carlo (UFMC), Parallel Replica Dynamics (PRD), and Adaptive Accelerated ReaxFF Reaction Dynamics (aARRDyn). These methods enhance the ability to simulate rare events and kinetic processes that are otherwise inaccessible to traditional molecular dynamics (MD) simulations. Additionally, improvements in charge description, such as the incorporation of ACKS2, have enhanced the accuracy of ReaxFF in describing electronic interactions and physisorption processes. Future developments of ReaxFF aim to improve its ability to model interfacial chemistry in batteries and structural/polarization behavior in piezoelectric and ferroelectric materials. The introduction of explicit electron description (eReaxFF) allows for more accurate simulations of electron affinity in radical species, providing a significant improvement over standard ReaxFF. Ongoing efforts focus on optimizing ReaxFF parameters and expanding its applications to modern architectures, making it more accessible and efficient for a wide range of scientific and engineering applications.