This paper examines in detail the phase behaviour of blends of alpha-methylstyrene/acrylonitrile copolymers (alpha-MSAN) with poly(methyl methacrylate) (PMMA), tetramethylbisphenol A polycarbonate (TMPC), poly(vinyl chloride) (PVC), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), poly(epsilon-caprolactone) (PCL) and bisphenol A polycarbonate (PC), and compares these with the corresponding behaviour of blends based on styrene/acrylonitrile copolymers (SAN). Replacement of styrene with alpha-methylstyrene widens the miscibility window with PMMA and PVC but narrows the miscibility window with TMPC. In addition, the phase separation temperatures for alpha-MSAN blends with PVC are higher while those with PMMA and TMPC are lower compared to similar SAN-based blends. PPO, PCL and PC were found to be not miscible with any of the alpha-MSAN copolymers. Interaction parameters for these systems were evaluated where possible from their lower critical solution temperature type phase boundary using the lattice fluid theory of Sanchez and Lacombe. The interactions between various monomer unit pairs were deduced using a binary interaction model for copolymers. The interaction parameters obtained are translatable from one system to another. The results are discussed in terms of interactions between monomer unit pairs and equation-of-state or compressibility effects.