An investigation of sintering kinetics of boron and boron carbide is presented. The influence of the powder size distribution on the temperature dependence of sintering, on reaching a high final density, and on gaining a homogeneous grain size has been shown. The results on the α-rhombohedral usage in reaction sintering for boron carbide production have been given. With the example of boron, the maximum sintering density was reached as the process was managed under the conditions providing the successive phase transitions in boron, Bamorph.→Bα→Bβ. The results of sintering of boron and boron carbide pellets compacted by explosive compression have been considered. Explosive pressing–sintering produces pellets of amorphous and α-rhombohedral boron.