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SUMMARYA generic, mass conservative local grid reÿnement technique for the lattice-Boltzmann method (LBM) is proposed. As a volumetric description of the lattice-Boltzmann equation is applied, mass conservation can be imposed by allowing the lattice-Boltzmann particles to move from coarse grid cells to ÿne grid cells and vice versa in the propagation step. In contrast to most existing techniques, no spatial and temporal interpolation of particle densities is applied. Moreover, since the communication between the coarse and the ÿne grids is independent on the collision step, the method can be used for any LBM scheme.It was found that the method is second-order accurate in space for 2-D Poiseuille ow and di erent grid setups. The method was also applied to the case of 2-D lid driven cavity ow at Re = 1000, where half of the cavity was locally reÿned. It was found that the locations of the two lower vortices could be captured accurately. Finally, a direct numerical simulation (DNS) of turbulent channel ow at Re = 360 was performed where the grid was locally reÿned near the walls of the channel. Good ÿrst-and second-order turbulence statistics were obtained, showing the applicability of the local grid reÿnement technique for complex ows.