X‐ray studies have been made of a number of carbon blacks, prepared under different conditions, and subject to various heat treatments. The patterns were made in evacuated cameras, using CuK&agr; radiation monochromated by reflection from rocksalt. The patterns consist of crystalline reflections (00l), and two‐dimensional lattice reflections (hk). The structure is one of true graphite layers arranged roughly parallel and equidistant, but otherwise completely random. The dimensions within a layer are the same as in graphite; the layer separation is somewhat larger than in graphite. The effect of heat treatment is to increase the size of the parallel layer groups. At graphitization the material changes discontinuously to the crystalline graphite structure. The usual carbon black is not finely divided graphite. Small angle scattering studies indicate the existence of clusters a few hundred angstroms in size. It is these clusters which are measured by microscope counts, by the electron microscope, and by surface areas, rather than the much smaller parallel layer groups.