Experimental soil mechanics has evolved through a continuous and reciprocal interaction with theory and geotechnical practice. This paper reviews that evolution as a history of ideas, highlighting how theoretical advances have driven new experiments and how improved testing techniques have reshaped theory. Starting from the limited tools available around 1925, we trace key developments up to 1950 and the emergence of Critical State Soil Mechanics, which unified deformation and failure and transformed data interpretation. Rather than providing an exhaustive inventory, we focus on eight major areas of progress since the 1950s: control of general stress and strain states, soil fabric, partially saturated soils, small-strain stiffness, strain localization, coupled thermo-hydro-chemo-biological processes, experimental micromechanics, and X-ray tomography. We conclude with some final reflections.