GROMACS is a widely used open-source software for molecular dynamics simulations, supporting a range of calculation types, including energy minimization, normal-mode analysis, and simulated annealing. Version 5 introduces significant performance improvements through advanced parallelization techniques, including SIMD registers, multithreading, heterogeneous CPU-GPU acceleration, and domain decomposition. The software supports a variety of simulation methods, including replica exchange, metadynamics, and alchemical free-energy transformations. GROMACS is available under the LGPLv2.1 license and supports multiple platforms, including CPUs, GPUs, and embedded systems. It provides a flexible and efficient compressed trajectory storage format, TNG, and supports a wide range of molecular mechanics force fields. The software is designed for high performance and efficiency on all hardware, with a focus on minimizing resource usage to maximize simulation throughput. GROMACS 5 includes a new C++ framework for analysis tools and supports parallel analysis of trajectory frames. It also includes new simulation features such as a Lennard-Jones PME implementation, Andersen-style thermostats, and adaptive resolution sampling. The software is highly scalable, with performance improvements on both CPU and GPU systems. GROMACS is used in a wide range of scientific applications, including studies of proteins, membranes, and ion channels. The software is supported by a large community of developers and users, and is continuously updated with new features and improvements.GROMACS is a widely used open-source software for molecular dynamics simulations, supporting a range of calculation types, including energy minimization, normal-mode analysis, and simulated annealing. Version 5 introduces significant performance improvements through advanced parallelization techniques, including SIMD registers, multithreading, heterogeneous CPU-GPU acceleration, and domain decomposition. The software supports a variety of simulation methods, including replica exchange, metadynamics, and alchemical free-energy transformations. GROMACS is available under the LGPLv2.1 license and supports multiple platforms, including CPUs, GPUs, and embedded systems. It provides a flexible and efficient compressed trajectory storage format, TNG, and supports a wide range of molecular mechanics force fields. The software is designed for high performance and efficiency on all hardware, with a focus on minimizing resource usage to maximize simulation throughput. GROMACS 5 includes a new C++ framework for analysis tools and supports parallel analysis of trajectory frames. It also includes new simulation features such as a Lennard-Jones PME implementation, Andersen-style thermostats, and adaptive resolution sampling. The software is highly scalable, with performance improvements on both CPU and GPU systems. GROMACS is used in a wide range of scientific applications, including studies of proteins, membranes, and ion channels. The software is supported by a large community of developers and users, and is continuously updated with new features and improvements.