In researching Conan of Caledonia, I scoured through my collections of Robert E. Howard's work for anything even vaguely related to Scotland & the Scots. Obviously the Bran Mak Morn tales, several historical adventures, the Pictish Conan adventures, & certain individual stories sprang to mind immediately. But the more I pored over the collections, the more of Scotland I found. Some of them are oblique references, perhaps even a single word or name - but once I get started on something, well, "Wha wul ti Cupar maun ti Cupar." For completeness' sake, I am indeed including the Picts of every time period, for the simple reason that Brule, Kelka, Zogar-Sag, & all the other Picts can ultimately claim their literary ancestry back to the Picts of Scotland. Howard himself does in "Kings of the Night," after all.
I've arranged the following catalogue in general written order, with Rusty Burke's essential Fiction & Verse Timeline & Paul Herman's indespensible Howard Works to sort them as best as I can.