Provided are a curable composition capable of both exhibiting a low shrinkage percentage during curing and forming a cured product having a low elastic modulus under high temperature conditions, a cured product of the curable composition, and a semiconductor encapsulating material and a printed wiring board which are produced using the curable composition. The curable composition includes an active ester compound (A) that is an esterification product of a phenolic compound (a1) and an aromatic polycarboxylic acid or an acid halide thereof (a2); and a curing agent. Also provided are a cured product of the curable composition, and a semiconductor encapsulating material and a printed wiring board which are produced using the curable composition.