VORO++ is an open-source C++ library for computing Voronoi tessellations, developed by Chris H. Rycroft. It is designed for large-scale three-dimensional research problems requiring flexibility. The library is structured around several C++ classes and is easy to modify and integrate into other programs. VORO++ uses a direct method to compute each cell individually, which is useful for physical applications that rely on cell-based statistics. It can handle complex boundary conditions, including plane walls (Fig. 1) and curved surfaces (Figs. 2 and 3), and deals with truncation errors in floating-point arithmetic. It can natively handle degenerate cases where Voronoi cells with high-order vertices may form. The library also supports neighbor calculations and tessellations for polydisperse particle packings (Fig. 4). Since each cell is computed individually, it is straightforward to generalize to a multicore architecture and achieve very high parallel efficiency. VORO++ is particularly useful in physics and materials science for analyzing particle systems, tracking density changes, and examining local neighbor relationships. While other mature software libraries exist, such as QHULL used by MATLAB, VORO++ is specifically designed for handling large-scale three-dimensional problems. The library is widely applicable in various fields due to its flexibility and efficiency in computing Voronoi tessellations.VORO++ is an open-source C++ library for computing Voronoi tessellations, developed by Chris H. Rycroft. It is designed for large-scale three-dimensional research problems requiring flexibility. The library is structured around several C++ classes and is easy to modify and integrate into other programs. VORO++ uses a direct method to compute each cell individually, which is useful for physical applications that rely on cell-based statistics. It can handle complex boundary conditions, including plane walls (Fig. 1) and curved surfaces (Figs. 2 and 3), and deals with truncation errors in floating-point arithmetic. It can natively handle degenerate cases where Voronoi cells with high-order vertices may form. The library also supports neighbor calculations and tessellations for polydisperse particle packings (Fig. 4). Since each cell is computed individually, it is straightforward to generalize to a multicore architecture and achieve very high parallel efficiency. VORO++ is particularly useful in physics and materials science for analyzing particle systems, tracking density changes, and examining local neighbor relationships. While other mature software libraries exist, such as QHULL used by MATLAB, VORO++ is specifically designed for handling large-scale three-dimensional problems. The library is widely applicable in various fields due to its flexibility and efficiency in computing Voronoi tessellations.