It is now fully accepted that industrial processes involving particulate systems are in the mainstream of chemical engineering practice, research and education. A scientific approach to particle processing implies the study and development of means for characterizing particles, the primary characteristic being particle size and distribution. This paper, by members of the EFCE working party on Characterisation of Particulate Solids is intended to give an overview of the evolution of the subject and some ideas on future developments. Comparison is made of the content of the Particle Size Analysis Conference of 1970 (PSA 1970) with that of the Particulate Systems Analysis Conference held in 2003 (PSA 2003). This shows the move away from absolute methods to more rapid secondary methods such as light scattering. Further modern developments are the application of in-line measurement for understanding industrial processes and their modelling, and the growth of image-based systems and tomography applied to industrial processing. Finally there is renewed interest in methods for sub-micron particle sizing for nanotechnology.