We examine the consequences of tidal interaction between eccentric short-period extrasolar planets and their host stars and of secular perturbations between planets in a given system. If the planet is within 0.05 AU of the star, the dissipation of the stellar tidal disturbance within the planet provides a significant energy source, which causes the planet to inflate as it adjusts to a thermal equilibrium. We determine the planetary size as a function of the tidal dissipation rate with or without the presence of a core. Inflation intensifies the star-planet tidal interaction and accelerates the pace of the planet's spin synchronization and orbital circularization. We apply our results to three systems with short-period planets: HD 209458, Ups And, and Tau Boo. University of California Observatories, Lick Observatory Bulletin, No. 139P.