Chichester Cathedral, the construction of which commenced between 1076- 90, within the rural setting of Sussex, is composed of an eclectic mix of limestones and some sandstones, which have undergone continued replacement over the lifetime of the building due to surface decay and failure. The purpose of this study was to map and record the decay exhibited on a southern aspect of the building, which was due for restoration. In addition a simple study was also undertaken on the early stone still existing from the first building phase from other areas of the building and within differing environments and which confirmed that decay forms commenced with a change in limestone type used, particularly in this case from the Quarr stone to the more micro porous Caen and similar limestones. Thus indicating porosity as a factor in weathering. Laboratory analysis of samples was not available for this study so the majority of observations and recordings were made on site. A study of the climate of the region in chapter 2, indicated that although rainfall for the region was low, humidity was relatively consistent and within the upper range (60-90 per cent). Although wind direction was mainly from the southwest, thereby removing any significant pollutants, the combination of low S02 and high humidity would fit in with the accepted environment for absorption of atmospheric salts and associated crystallisation, hydration pressure and expansion, leading to decay. Micro-climate analysis of an area of the southern side also confirmed that the moisture content across the stone face was also conSistently high and thus an indicator of a salt mobilisation and hydration environment. Chapter 3, which considers the building phases and materials used throughout the building history of the Cathedral, also mapped an emerging pattern of stone life for the various parts of the Cathedral, which tends to fit in with the theory that the lithology of the same stone type may playa significant factor inIt is well established that atmospheric pollution is a major contributor to stone decay but no major polluting industrial base has ever existed within the area of Chichester, which was primarily an agricultural centre (historically a 'Staple Town'). It was necessary therefore to establish the possible historic forms of industry that may have contributed in some way to atmospheric pollution thereby enabling the mapping of resultant pollution levels over time. The analysis of this industry in chapter 4 has indicated that as expected the levels of S02 were so low as to be almost inSignificant until the arrival of wide spread coal use, and then even then they were very low. The amount may be significant, however, when combined with high relative humidity. The actual mapping and main photographic analysis of surface conditions across three height ranges is undertaken and described in chapter 5. In a number of cases, a relationship between black crusting and surface loss could not be established, although, it was apparent that scaling and surface loss of the sample areas was high. It became significant that decay was tending to emanate from the lime mortar joints in a number of locations and situations. This also became evident when looked for in other regions of the structure, for example the north side of the Bell Tower, which had started to decay within a forty-year period of restoration and is covered in chapter 6. Various forms of mechanical breakdown were established but this research did not enable any form of biological decay analysis to be undertaken. the durability of samples.