A curable polymer composition comprising: (A) a thermoset maleimide resin precursor component; and further comprising one or both of: (B) an arylsulphone-containing maleimide component; and (C) a polyarylpolymer thermoplastic toughening agent component, wherein in the absence of component (B), said component (C) comprises one or more maleimide pendant and/or end groups, and thermoset resins and composites derived therefrom.