A general theory of spray (or other particle) flows is proposed. It is based on the approximations that the particles in the flow may be treated as points which displace no volume, are adequately described by use of a particle state vector, and which undergo instantaneous transitions between states. The flow in which these particles are embedded is assumed to be a space-filling continuum, describable at the level of the Navier-Stokes equations. Consideration of the information content of such a flow leads to definition of a phase space in which any spray flow will occupy a unique location at any instant in time. By computing the number density of such system points in this space, and deriving a transport equation for that number density, the evolution of any distribution of spray flows may, in principal, be solved for at all subsequent times.