To provide a flame-retardant curable composition which exhibits excellent electrical properties, good solvent resistance, and good thermal expansion characteristics.

This curable composition is formulated from an epoxy resin; a flame-retardant additive essentially free of phenolic groups and of epoxy groups; and a thermoplastic resin. The preferred epoxy resin is a mixture of an epoxy resin having less than 2 glycidyl ether groups per molecule and an epoxy resin having more than 2 glycidyl ether groups per molecule. The preferred flame-retardant additive is a brominated heterocyclic compound, still preferably a brominated triazine compound. The preferred thermoplastic resin is a poly(phenylene ether). This composition advantageously can be combined with a reinforcement in the manufacture of circuit boards having excellent electrical properties, good solvent resistance, and good thermal expansion characteristics.