This thesis presents a study into the influence of suction on the compressibility and swelling characteristics of a broad range of reconstituted clay soils. Soil water relationships are explored, discussing evaporation, shrinkage, swelling and the development of suction. A comprehensive review of suction measurement techniques is detailed, identifying operating principles, performance and limitations of each technique. For the main experimental programme a new, osmotically suction controlled oedometer has been developed. The oedometer utilises the osmotic potential of a large molecular weight salt (polyethylene glycol) across a semi-permeable membrane to control matrix suctions in the sample during testing. Independent continuous measurement of the suction in the sample during testing is made using the Imperial College tensiometer. Four materials have been assessed. Kaolin, London clay, and two expansive soils from Kenya. A series of suction controlled stress path tests were carried out on the four materials. In addition intrinsic and soil moisture characteristics were determined and discussed. Routine soil classification tests, mineralogy and SEM studies were also carried out. The results are presented and discussed, and recommendations for future research made.