LaGriT — Los Alamos Grid Toolbox. LaGriT is a library of user callable tools that provide mesh generation, mesh optimization and dynamic mesh maintenance in two and three dimensions for a variety of applications. Geometric regions within arbitrarily complicated geometries are defined as combinations of bounding surfaces, where the surfaces are described analytically or as tessellated surfaces (triangles and/or quadrilaterals). A variety of techniques for distributing points within these geometric regions are provided. Mesh generation uses a Delaunay tetrahedralization algorithm that respects material interfaces. The data structures created to implement this algorithm are compact and powerful and expandable to include hybrid meshes (tet, hex, prism, pyramid, quadrilateral, triangle, line) however the main algorithms are for triangle and tetrahedral meshes. Mesh refinement, derefinement and smoothing are available to modify the mesh to provide more resolution in areas of interest. Mesh refinement adds nodes to the mesh based on geometric criteria such as edge length or based on field variable shape. Mesh elements may become distorted as mesh nodes move during a time criteria such change in field. Mesh smoothing moves nodes to adapt the mesh to field variable measures, and, at the same time, maintains quality elements. During time dependent (Lagrangian moving mesh) simulation or when nodes are added as a result of refinement operations, mesh reconnection via a series of edge flips can be used to eliminate highly distorted elements.