The dominantly lacustrine Middle Old Red Sandstone strata of northern Scotland have long been famed for their remarkable cyclicity. The regional extent, character, controls and periodicity of the cycles have been investigated. The Middle Old Red Sandstone of northern Scotland largely reflects deposition within a closed lake basin (the Orcadian Basin). Regular fluctuations in lake level responding to climatic forcing, resulted in the deposition of cyclic sequences which are recognised from Easter Ross, in the south west, throughout Caithness and up to Orkney in the north east.