This thesis aims to develop an understanding of the relationship between climate, topography and glacier fluctuations in Iceland. A mass balance/glacier flow model is applied to the Holocene fluctuations of Sólheimajökull, an outlet glacier in southern Iceland. The model is also used to predict the response of Sólheimajökull to future climatic warming. The findings provide insight into the spatial variability of glacier fluctuations in Iceland, and the dynamics of Holocene climatic changes in the North Atlantic. The results from the model suggest that the response of Icelandic glaciers to climatic change can be related to glacier area-altitude distribution. Outlet valley glaciers located in high precipitation areas descend to elevations of 0-100 m where air temperature is mild. Ablation occurs throughout the year and glacier mass balance has a large amplitude response to temperature variations. Furthermore, outlet valley glaciers experience dynamic length variations in response to climatic change. This is a geometric effect where small changes in ice cap volume result in significant fluctuations in glacier lengths. In contrast, wide ice cap lobes in central Iceland exhibit a different response to climatic change. Precipitation levels are lower and glaciers terminate at altitudes of 600-800 m. Ablation is restricted to the summer months, and glacier mass-balance has a lower amplitude response to temperature variations. In addition, ice cap lobes experience smaller dynamic length fluctuations in response to climatic change. This is because ice cap margins undergo small changes in extent to response to changes in glacier volume. Finally, where ice cap lobes terminate on sandur plains, further advance leads to glacier widening and an unsustainable increase in ablation. The numerical model is used to successfully reconstruct Holocene climatic changes over the last 5000 years from the record of glacier length variations in Sólheimajökull.