In a powder, each particle is different and it is the distribution of the properties of the particles which distinguish one sample from another. A powder process that seeks to change the distribution in a controlled manner, and the necessary model which describes the change, is known as a population balance. The creation of such a model is essential to the design and control of processes such as grinding, crystallisation, and granulation. The basic ideas underlying population models were established at a time when the numerical capability to solve them was much less than it is today. In this perspective article, it is suggested that the population model should be simpler in concept but more ambitious in purpose if full advantage is to be gained from the modem computing capability.