The primary objective of this thesis is to investigate whether Irish climate is changing, and if so, what are the possible driving forces of this change. Analyses of surface climate records appear to support global trends. Annual temperature records indicate an increase of 0.5°C since the beginning of the 20th century, with more rapid warming in the past three decades. Irish precipitation changes are also consistent with the predictions of Global Climate Models (GCMs), with evidence of a shift towards winter increases. Other important trends include a decrease in frequency of frost days and an increase in frequency of wet and rain days in certain months of the year. An important element of the research, therefore, is to investigate what is steering this change in climate. A circulation-type catalogue for Ireland has been constructed from National Centers for Environmental Prediction (NCEP) Reanalysis data, to objectively classify atmospheric circulation patterns. It is thus possible to determine to what extent the changing frequency of circulation types is influencing the spatial and temporal variability of the local climate. As a further step, by using the HadCM3 GCM data for the 2041-2070 period, it is possible to outline what changes in frequency of circulation types may be expected to occur with respect to the emission scenarios. Based on the relationships derived in the present, between CTs and precipitation, these can be applied to future CT frequencies to derive precipitation scenarios. The seasonal precipitation changes found are most likely attributed to changes in the westerly and southwesterly flow, associated with a shift in the North Atlantic Oscillation Index.