Solutions for soil engineering and soil-structure interaction problems need realistic and pertinent experimental and modelling tools. In this work, extensive developments proposed by the invited speakers of the Lyon International Symposium held in September 2003 are presented, including experimental investigations into deformation properties; laboratory, in-situ and field observation interpretations; behaviour characterisation and modelling; and case histories. The contributions include recent investigations into anisotropy and non-linearity, the effects of stress-strain-time history, ageing and time effects, yielding, failure and flow, cyclic and dynamic behaviour. In addition, advanced geotechnical testing is applied to real engineering problems, and to ways of synthesising information from a range of sources while engaging in practical site characterisation studies.