The purpose of this thesis has been primarily to show that harsh periglacial conditions have prevailed in Scotland during the last glacial retreat, and that less severe periglacial conditions still exist on high ground. The distinctive geomorphic agencies associated with these conditions have been discussed, together with their effects on the landforms. After an introductory section outlining the main ideas in periglacial studies, and presenting the proposed chronological framework based on studies of glacial moraines and pollen analysis, the evidence for cryoturbation in Scotland is presented. Consideration of the fossil wedges and involutions to be found in unconsolidated material in Scotland has shown that very severe climatic conditions with permafrost prevailed to the very end of the ice age. Contemporary cryoturbation exists today on high ground but is of a superficial type associated with a much milder climate. The severe climate in the past has led to extensive shattering of the bedrock in areas that were not shielded by overlying ice or glacial drift. The presence of the resulting angular loose rock debris and of permafrost greatly favoured periglacial mass wasting and solifluction deposits are widespread, especially in the E. of the country. The work of running water seems to have been mainly the evacuation of the debris furnished from the slopes by frost shattering and solifluction. Wind did not play an Laportant role. The effectiveness of the modification of the landforms induced by periglaciation is shown to depend not only on the nature of the rock and the duration and intensity of the cold climate, but also on the nature of the pre-existing landscape. Modification has gone furthest in NE. Scotland and in the Eastern parts of the Southern Uplands where chemically rotted and fissile rocks respectively have assisted the work of fairly prolonged frost shattering. The forms produced include altiplanation benches, niches, tors, straight slopes of mass wasting and trough-like valleys. Corresponding to this erosion, important gravel accumulations have developed at the margins of hill masses and on the floors of main valleys. In the heavily glaciated W. of the country, periglaciation has done little to modify the landforms and indeed throughout Scotland has only retouched a landscape that is the work of agencies associated with other climates. The mild variety of periglaciation prevailing today on high ground has produced a wide variety of mass wasting forms, including lobes, terraces and block streams which can with difficulty be distinguished from the features initiated under more extreme climatic conditions in the past. Contemporary mass movement and disturbance of the ground by frost is most marked in areas where the vegetation is scanty and it has been shown that one of the main factors in restricting its growth on hill tops is wind. Consequently the lower limit of very active periglaciation today is much nearer sea level in the 14. and rises progressively SE. ward. It is concluded that the study of periglaciation in Scotland is of the greatest significance for an understanding of the Pleistocene history of the country and the evolution of the soils.