Lagrange is a comprehensive C++ geometry processing library focused on 3D mesh manipulation, analysis, and visualization. It provides a robust core mesh data structure (SurfaceMesh) with extensive algorithms for mesh processing including subdivision, simplification, cleaning, remeshing, and parameterization. The library features specialized modules for geodesic computation, texture processing, volume conversion, boolean operations, and more, along with UI/viewer components for interactive visualization and Python bindings for scripting. Built with a modular architecture using modern C++ template metaprogramming, it emphasizes algorithmic correctness through exact predicates and supports multiple mesh formats via Assimp integration.