The magic of sands — The 20th Bjerrum Lecture presented in Oslo, 25 November 2005This paper represents the written version of the 20th Bjerrum Lecture. While it has been edited for the present publication, it retains the general structure of the original lecture, which was intended for a general geotechnical audience. It deliberately points out some of the still-open questions concerning soil modelling. The Bjerrum Lecture is presented in Oslo in alternate years by the Norwegian Geotechnical Society with the support of the Bjerrum Memorial Fund (Laurits Bjerrums Minnefond).