We report on the discovery and confirmation of Kepler-7b, a transiting planet with unusually low density. The mass is less than half that of Jupiter, M P = 0.43 M J, but the radius is 50% larger, R P = 1.48 R J. The resulting density, ¿P = 0.17 g cm–3, is the second lowest reported so far for an extrasolar planet. The orbital period is fairly long, P = 4.886 days, and the host star is not much hotter than the Sun, T eff = 6000 K. However, it is more massive and considerably larger than the Sun, M = 1.35 M and R = 1.84 R , and must be near the end of its life on the main sequence