AbstractThe collection of papers in this volume results from a joint meeting of the Tectonic Studies Group and the British Sedimentological Research Group of the Geological Society of London, held at the University College of Wales, Aberystwyth on 10–12 April 1986. About half the papers presented at that meeting were offered for publication. A report of the full proceedings has appeared in the Journal of the Geological Society (Fitches and Woodcock 1986) as have abstracts of all the contributions.The stimulus for the conference was the recent upsurge in structural and sedimentological research in Wales, following and partly stimulated by new work on Welsh volcanic rocks (reviews by Allen 1982; Bevinset al.1984; Kokelaaret al.1984). The papers here reflect the breadth as well as the quantity of the activity, particularly in previously underresearched areas such as the Mid Welsh Late Ordovician to Early Silurian sedimentary rocks.The papers are arranged in approximate time order of the events they describe. Naturally those on sedimentation in the Early Palaeozoic basin precede those concentrating on Caledonian basin inversion and deformation. The areas that they describe are located on Figure 1. Here we briefly set the papers in their regional context and suggest some tentative conclusions that can be drawn from the conference presentations as a whole. More extensive reviews of sedimentation and/or tectonics in the Welsh basin are given by Coward and Siddans (1979), Hollandet al.(1979), and Woodcock (1984