μ-diff - An open Matlab toolbox for solving multiple scattering problems by disks. Multiple scattering is a highly complex wave problem that finds great applications in many areas of physics and engineering (acoustics, electromagnetism, optics, nanophotonics, elasticity...). μ-diff (acronym for multiple-diffraction) is an open-source Matlab toolbox for solving multiple scattering problems by clusters of circular cylinders. Any distribution of the cylinders is possible, deterministic or random, allowing to define basic to complex disordered media. The rigorous mathematical formulation is based on the integral equations formulations. The finite-dimensional approximation technique is a Fourier spectral method combined with linear algebra solvers (direct gaussian elimination method or preconditioned Krylov subspace iterative techniques). Pre- and post-processing facilities are included in μ-diff. Since integral equations are used, many direct and inverse wave scattering problems can be solved with μ-diff. Examples of scripts are provided with the toolbox.