GROMACS is a widely used open-source software for molecular dynamics simulations, offering a rich set of calculation types, preparation, and analysis tools. Version 5 of GROMACS introduces significant performance enhancements through multi-level parallelism, including SIMD registers, multithreading, heterogeneous CPU-GPU acceleration, advanced 3D domain decomposition, and ensemble-level parallelization. The software supports various simulation methods, force fields, and ensemble techniques, and is designed to run efficiently on a wide range of hardware, from laptops to supercomputers. Key features include a new Lennard-Jones particle-mesh Ewald (PME) implementation for accurate long-range electrostatics, a flexible compressed trajectory storage format, and a parallel analysis framework for developing new tools. Performance benchmarks demonstrate substantial improvements in both single-core and heterogeneous system scaling, highlighting the software's robustness and efficiency across different hardware architectures.GROMACS is a widely used open-source software for molecular dynamics simulations, offering a rich set of calculation types, preparation, and analysis tools. Version 5 of GROMACS introduces significant performance enhancements through multi-level parallelism, including SIMD registers, multithreading, heterogeneous CPU-GPU acceleration, advanced 3D domain decomposition, and ensemble-level parallelization. The software supports various simulation methods, force fields, and ensemble techniques, and is designed to run efficiently on a wide range of hardware, from laptops to supercomputers. Key features include a new Lennard-Jones particle-mesh Ewald (PME) implementation for accurate long-range electrostatics, a flexible compressed trajectory storage format, and a parallel analysis framework for developing new tools. Performance benchmarks demonstrate substantial improvements in both single-core and heterogeneous system scaling, highlighting the software's robustness and efficiency across different hardware architectures.