The purpose of this review paper is to identify and outline some critical questions about the geology and tectonic evolution of the Scottish Caledonides in their wider Caledonian/Appalachian context. We outline what we think we know and what we perceive to be some important problems from about 1.0 Ga (Grenville Orogeny) to the Middle Devonian (Acadian Orogeny). We do not attempt in-depth analyses of any terrain or tectonic topic in this review but, mainly, pose questions. Scotland is considered in the context of the Irish Caledonides and the Northern Appalachians, especially Newfoundland, so we make reference to these areas where appropriate. Each section is intended as ‘stand-alone’, not dependent upon prior or subsequent sections; the sequence of sections, roughly in time order, has a historical narrative thread. We have not included cross-sectional schematic diagrams because we do not have a clear picture of plate boundary zone and terrane arrangements in the Caledonides. There are too many enigmas, paradoxes and unknowns to draw tectonic cross-sections with conviction.