Abstract: A composition for film formation which can form a film suitable for use as an interlayer dielectric in a semiconductor device, etc. and having an appropriate even thickness and can give a film having excellent characteristics including permittivity and Young's modulus; and a dielectric film obtained from the film-forming composition. The composition contains a compound (X) having a functional group which is partly eliminated by heating, irradiation with light, irradiation with radiation, or a combination thereof to generate volatile matter and yield an unsaturated group in the remaining part of the functional group.