Multi-proxy palaeoecological analyses were conducted on late Holocene cores taken from six sites in Cumbria. The project had three major objectives: to study regional abandonment phases during the Medieval era (particularly in the 14th century AD), to rigorously test the possible impact of environmental changes (climatic deterioration and soil nutrient depletion) on any such phases, and to investigate the potential of diatoms as alternative proxy indicators of human impact. Two major Medieval abandonment phases were identified in the pollen spectra. One in the late 9th century AD was extremely widespread and associated with substantial woodland regeneration - suggesting the near-total abandonment of extensive areas of the county during this period. This phase can probably be linked to the Danish invasion of Cumbria in the 870s. Another decline in the 14th century AD was more subtle, only affecting arable-type indicators; pollen records from this period suggest a general reduction of population rather than complete regional abandonment. Plant macrofossil and humification data from Walton Moss and Hulleter Moss showed three major episodes of climatic deterioration in the Medieval era (AD 920-970, AD 1160-1190 and AD 1370-1430). Only the 14th century decline had any discernible impact on settlement patterns. Surprisingly, the more populous lowland sites appeared more vulnerable to climatic forcing during this phase. These results suggest that traditional conceptions of marginality are misleading, and that lowland Medieval communities were actually more vulnerable to environmental impacts due to their low levels of economic and ecological diversity. Tests at Mockerkin Tarn on the impact of catchment nutrient depletion were inconclusive. Geochemical and diatom data showed a significant decline in catchment phosphorus from AD 450-1000, but this had no definite impact on land-use patterns.