The mechanism of formation, and the chemical and hydrate forming properties of the 1,8-terpins are discussed. Configurations are assigned to the six 1,8-dihalogeno-p-menthanes, ethylnopinol, β-terpineol, p-menthan-1-ol, and homoterpin. It is suggested that the presently accepted configurations of the carveols and sobrerols may need to be reversed and that the structures of the p-menthane-2,8-diols need revision.