The Fourth Conference on Particle-Based Methods (PARTICLES 2015) will be organised on 28-30 September 2015 in Barcelona, Spain. The previous three conferences on this series were held in Barcelona on 25-27 November 2009 and 26-28 October 2011, and in Stuttgart on 18-20 September 2013. PARTICLES 2015 will address both the fundamental basis and the applicability of state-of-the-art particle-based computational methods that can be effectively used for solving a variety of problems in engineering and applied sciences. The denotation "Particle-Based Methods" basically stands for two different computational models in solid and fluid mechanics. On the one hand it represents discretization concepts in which the response of a continuum is projected onto "particles" carrying the mechanical information during deformations. Typical representatives are Meshless Methods, Smoothed Particles Hydrodynamics (SPH), Moving Particle Simulation (MPS), Particle Finite Element Method (PFEM), Material Point Method (MPM) and the Lattice-Boltzmann-Method (LBM). On the other hand the notion expresses the computational representation of physical particles existing on different scales. Classical versions are Molecular Dynamics (MD) or the Discrete (Distinct) Element Method (DEM). Here either the particles exist a priori like in granular matters or they evolve during the loading process. In some cases the two models of discretization and physical particles are even interconnected. PARTICLES 2015 covers both concepts because of their strong interrelation in their computation as well as application point of view.