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Desiccation of clay soil caused by vegetation - grass, bushes and trees - and its effects on the stability of slopes, buildings, roads and other structures has long been a topic of interest and concern to the geotechnical engineer. Several international symposia on the topic have been held during the past 60 years, and the literature on the subject is voluminous. A review of past studies of soil desiccation and its effects showed that, with few exceptions, investigations had been of a short-term nature and had not adequately considered the variable annual effects of atmospheric and hydrological causes of soil desiccation and rehydration. As a contribution to providing this longer-term information, it was decided to embark on an extended study of the effects of evapotranspiration by vegetation and atmospheric climate on the seasonal and year-to-year variation of soil water content. The study is now complete and this paper presents an overview of the investigation from 2000 to 2006, including the influence of annual weather variations on the desiccating effects of lines of trees and bushes, the potential effects of desiccation caused by single trees on adjacent buildings, and the portrayal of these effects by means of soil water content and storage profiles, and soil water balances.