Many materials containing colloids or polymers are polydisperse: they comprise particles with properties (such as diameter, charge, or polymer chain length) that depend continuously on one or several parameters. This effectively infinite number of distinguishable particle species makes the theoretical prediction of phase equilibria a highly non-trivial task. We give an overview of recent progress, focussing on the "moment free energy" method which reduces the problem to one involving only the densities of a finite number of quasi-species. Applications to isotropic-nematic phase equilibria of rod-like particles and to the phase behaviour of polydisperse hard spheres are described. (C) 2003 Elsevier B.V. All rights reserved.