Regular polyhedra generalize the notion of a regular polygon to three dimensions. A regular polyhedron is a polyhedron with congruent faces and identical vertices. There are only five convex regular polyhedra, and they are known collectively as the Platonic solids, shown below. From the top left they are the regular tetrahedron (four faces), cube (six), octahedron (eight), dodecahedron (twelve), and icosahedron (twenty).