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MODPATH-LGR is a particle tracking post-processing program for computing three-dimensional flow paths for steady-state and transient groundwater flow in models with local-grid refinement (sometimes called embedded models). Locally refined grids consist of a larger regional-scale parent model and one or more smaller embedded local-scale child models. This program uses output produced by MODFLOWLGR, in which child grids in parent grids are refined by using the Shared-Node Local Grid Refinement (LGR) package of the three-dimensional finite-difference groundwater-flow model MODFLOW published by the U.S. Geological Survey (USGS). The particle tracking scheme is based on MODPATH, which uses an analytical expression for particle movement within each finite-difference cell. Particles are tracked among cells until discharged through model boundaries, weak sinks, or other designated discharge zones. MODPATHLGR tracks particles between the parent and child models by using flows calculated at the interface boundaries. Flows calculated by MODFLOW-LGR are modified to account for fractional finite-difference cells along the shared-node interface between parent and child models. Required program input includes standard MODPATH input files for the parent and child models and a MODPATH-LGR control file. This documentation describes how particles are transferred between parent and child models and demonstrates program operation with two hypothetical steady-state xsimulations.