Lactone-containing compounds having formula (1) are novel wherein R1 is H, F, methyl or trifluoromethyl, R2 and R3 are monovalent hydrocarbon groups, or R2 and R3 may together form an aliphatic hydrocarbon ring, R4 is H or CO2R5, R5 is a monovalent hydrocarbon group, W is CH2, O or S, and k1 is 0 or 1. They are useful as monomers to produce polymers which are transparent to radiation≦500 nm. Radiation-sensitive resist compositions comprising the polymers as base resin exhibit excellent properties including resolution, pattern edge roughness, pattern density dependency and exposure margin.