Stiffness parameters are required for many geotechnical calculations, including numerical modelling using the finite element or finite difference methods. The measurement of stiffness is not trivial, yet the actual values of stiffness adopted during analyses can have a very significant impact on predictions, and hence the perceived viability of a project. Measurement of stiffness in the laboratory is now well established, using techniques such as advanced triaxial testing with local strain measurement, cyclic triaxial testing, and the resonant column apparatus. Field geophysical techniques, although not as well established, can add significantly to the determination of input parameters for deformation analyses and prediction. This paper considers the strengths and weaknesses of these methods, using examples from a range of projects and ground conditions, and discusses how seismic geophysics can most effectively contribute.