The 2DECOMP&FFT library is a software framework written in modern Fortran to build large-scale parallel applications. It is designed for applications using three-dimensional structured meshes with a particular focus on spatially implicit numerical algorithms. However, the library can be easily used with other discretisation schemes based on a structured layout and where
pencil decomposition can apply. It is based on a general-purpose 2D pencil decomposition for data distribution and data Input Output (I/O). A 1D slab decomposition is also available as a special case of the 2D pencil decomposition. The library includes a highly scalable and
efficient interface to perform three-dimensional Fast Fourier Transforms (FFTs). The library has been designed to be user-friendly, with a clean application programming interface hiding most communication details from application developers, and portable with support for modern CPUs and NVIDIA GPUs (support for AMD and Intel GPUs to follow).