A brief history of diamond synthesis, as well as instrumentation capable of accomplishing the experiment, are given. The direct conversion of graphite to diamond by severe transient pressure and high adiabatic temperature is reviewed. Current tentative explanations of the mechanism are discussed. Studies performed at the U. S. Army Electronics Research and Development Laboratory on several metal-carbon, metal-carbon-silicate, and carbon-nonmetallic salt systems are described and data presented. A mechanism of formation is proposed for synthesis performed under relatively static high pressures and high temperatures; namely, crystallization from solution. Supporting evidence is given. The use of secondary chemical reactions in diamond formation processes also is described. A brief discussion is presented on correlation of laboratory data with the genesis of natural diamond.