This paper reviews some recent developments in molecular simulation methodologies for the determination of phase equilibria of polymeric and ionic systems. The chain increment method which is based on an extension of Widom’s test particle expression to polymeric systems can be used to calculate the chemical potentials of long chains. A recent calculation of vapor-liquid phase diagrams for a bead-spring polymeric model for chain lengths of 20, 50 and 100 based on this technique is described. The technique has also been applied to obtain the chemical potential and adsorption isotherms for confined polymers. For strongly interacting or associating fluids, such as ionic systems, conventional simulation algorithms fail because of the presence of large clusters that inhibit internal equilibration and particle transfers. Multiparticle moves and distance-biased pair transfers enable reliable calculations for such systems. Applications to calculation of phase coexistence for the restricted primitive model for ionic solutions are discussed.