The graphite --> diamond transition in the diamond stability field can be either direct or solvent-assisted. The direct transition may proceed by spreading a puckered basal plane of graphite in the direction perpendicular to it. The kinetics of such a transition may be approximated by the growth of a two-dimensional nucleus. The threshold temperature of the transition appears to depend on the degree of perfection of the original graphite. Hence, the more perfect the graphite is, the lower temperature it may transform into diamond. The solvent-assisted transition normally proceeds by rapid nucleation followed by growth of these nuclei. The kinetic model for continuous nucleation may be applied to the early stage of such transition. The activation energies for the transition can then be calculated, it is found that these activation energies seem to vary inversely with the solubility of carbon in these solvents at ambient pressure. Hence, the higher the amount of carbon a solvent dissolves at ambient pressure, the more effective it can be as a catalyst for the graphite --> diamond transition under high pressure.