Bark mills, also known as Catskill's mills, are water, steam, horse, ox or wind-powered edge mills used to process the bark, roots, and branches of various tree species into a fine powder known as tanbark, used for tanning leather. This powdering allowed the tannin to be extracted more efficiently from its woody source material. A barker would strip the bark from trees so that it might be ground in such mills, and the dried bark was often stored in bark houses.

Tanning, or hide tanning, is the process of treating skins and hides of animals to produce leather. A tannery is the place where the skins are processed.