The behaviour of particulate solids is complex and intriguing because it involves phenomena which operate on several different scales of length and time. Once this is recognized, it is obvious that particle technology must incorporate more than continuum and fluid mechanics. Because research in some areas is still at the level of attempting to identify the important phenomena, it is essential to design fundamental experiments and to try to avoid empirical characterization. Particle science has now developed to the point where it should start to impact on other areas of intellectual enquiry and human activity.