VORO++ is an open-source software library for computing the Voronoi tessellation, a method originally proposed by Georgy Voronoi in 1907. The library is designed specifically for large-scale three-dimensional research problems and is particularly useful in physics and materials science for analyzing particle systems, tracking density changes, and examining local neighbor relationships. VORO++ is built around several C++ classes, making it flexible and easy to modify and integrate into other programs. It employs a direct calculation method, allowing for tailored cell computation that can account for complex boundary conditions such as walls and curved surfaces. The library handles floating-point arithmetic errors and degenerate cases, supports neighbor calculations and polydisperse particle packings, and can be efficiently parallelized on multicore architectures. For more information, visit the VORO++ website at http://math.lbl.gov/voro++.VORO++ is an open-source software library for computing the Voronoi tessellation, a method originally proposed by Georgy Voronoi in 1907. The library is designed specifically for large-scale three-dimensional research problems and is particularly useful in physics and materials science for analyzing particle systems, tracking density changes, and examining local neighbor relationships. VORO++ is built around several C++ classes, making it flexible and easy to modify and integrate into other programs. It employs a direct calculation method, allowing for tailored cell computation that can account for complex boundary conditions such as walls and curved surfaces. The library handles floating-point arithmetic errors and degenerate cases, supports neighbor calculations and polydisperse particle packings, and can be efficiently parallelized on multicore architectures. For more information, visit the VORO++ website at http://math.lbl.gov/voro++.