Site characterisation and in situ test interpretation have been evolving from basic empirical recommendations to a sophisticated area demanding a thorough knowledge of material behaviour and numerical modelling. With the advent of modern testing techniques and more rigorous methods of analysis, site characterisation in natural soils is gaining momentum. This Report presents a critical appraisal in the understanding and assessment of the stress-strain-time and strength characteristics of natural soil conditions and explores new interpretation methods capable of measuring soil properties shaped by effects of microstructure, stiffness non-linearity, small and large strain anisotropy, weathering and destructuration, consolidation characteristics and rate dependency. Interpretation methods in different soil formations such as clay, sand, silt and bonded geomaterials are explored using different testing techniques. Since the in situ behaviour of natural soils is complex, a single general recommendation is to cross-correlate measurements from different tests. When data are combined there is more scope for rational interpretation and, for this reason, emphasis has been placed on correlations with mechanical properties that are based on the combination of independent measurements.