Particle　shape　governs　the　macro-mechanical　behavior　of　high　explosives.　This　study　develops　3D　computational　geometry　techniques　to　determine　commonly　used　sphericity　and　roundness　definitions　of　typical　high　explosive　particles,　including　HMX　(octahydro-1,3,5,7-tetranitro-　1,3,5,7-tetrazocine),　RDX　(1,3,5-Trinitroperhydro-1,3,5-triazine),　and　CL-20　(2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane).　This　technique　can　automatically　determine　principal　dimensions,　volume,　surface　area,　minimum　circumscribed　sphere,　maximum　inscribed　sphere,　and　the　3D　convex　hull　of　3D　particle　geometries　and　determine　commonly　used　3D　sphericity　descriptors　of　high　explosive　particles.　This　technique　can　also　automatically　identify　corners　on　the　3D　particle　surface,　fit　appropriate　spheres　to　these　corners,　and　compute　Wadell＇s　roundness　of　high　explosive　particles.　This　study　demonstrates　that　the　qualities　of　3D　particle　geometries　affect　the　computational　results　of　particle　sphericity　and　roundness　descriptors　of　high　explosives.　These　descriptors　display　a　hierarchy　of　resistance　to　the　effects　of　low　image　quality.　Therefore,　the　minimum　requirements　for　ensuring　reliable　shape　characterization　of　these　parameters　are　established　for　high　explosives.　This　study　systematically　compares　2D　and　3D　particle　shape　characterizations　of　around　15,000　particles　from　three　high　explosives　(HMX,　RDX,　and　CL-20).　Results　show　that　2D　sphericity　and　rounded　definitions　either　underestimate　the　corresponding　3D　definitions　or　vary　within　large　ranges　leading　to　uncertainties　for　inferring　3D　particle　characteristics　from　2D　images　of　high　explosives.