Scientific investigation of the Appalachian-Caledonide stratiform ores began more than 160 years ago and since that time has had an important influence on ideas concerning the nature, derivation, and mode of deposition of such ores all over the world.The layered and conformable nature of some of the Norwegian ores had been recognized by 1820 and of the Ducktown, Tennessee, deposits by 1855. The probable volcano-sedimentary (i.e., exhalative) identity of the Norwegian deposits had been recognized by 1873, and the fact that most of the Appalachian stratiform ores had been regionally metamorphosed was established by 1909.These early prognostications were overwhelmed by the "late-stage structurally controlled hydrothermal replacement" school between about 1900 and 1955. However, exhalative-sedimentary ideas began to reappear about 1956. Since that time, and largely as a result of the stimulus provided by the great discoveries in the Canadian Appalachians in the 1950s, understanding of the stratiform ore province of the Appalachian-Caledonide orogen, and of similar orogens and ores elsewhere, has advanced with great rapidity. This has involved not only the ores themselves but also their environments and has led to a much greater appreciation of the ores as petrogenetic entities in their own right and of their place and significance in crustal evolution. This in turn has led to a greatly increased sophistication in stratiform ore exploration technique.