Sintering mechanisms and kinetics were investigated for ZrB2 ceramics produced using reaction hot pressing. Specimens were sintered at temperatures ranging from 1800 degrees C to 2100 degrees C for times up to 120min. ZrB2 was the primary phase, although trace amounts of ZrO2 and C were also detected. Below 2000 degrees C, the densification mechanism was grain-boundary diffusion with an activation energy of 241 +/- 41kJ/mol. At higher temperatures, the densification mechanism was lattice diffusion with an activation energy of 695 +/- 62kJ/mol. Grain growth exponents were determined to be similar to 4.5, which indicated that a grain pinning mechanism was active in both temperature regimes. The diffusion coefficients for grain growth were 1.5x10(-16)cm(4)/s at 1900 degrees C and 2.1x10(-15)cm(4)/s at 2100 degrees C. This study revealed that dense ZrB2 ceramics can be produced by reactive hot pressing in shorter times and at lower temperatures than conventional hot pressing of commercial powders.