The Spitzer Space Telescope has allowed us to measure the atmospheric properties of transiting hot Jupiters, giant planets which pass in front of their host stars every few days, with three techniques: (1) the wavelength dependence of atmospheric absorption by the planet's atmosphere as it transits in front of its host star; (2) the emission spectrum of the planet measured as the planet passes behind the host star; and (3) the phase variation of the planet as the day and night sides rotate in and out of view. I will review recent results in this rapidly changing field, discuss the implications for the atmospheric dynamics and compositions of these planets, and look towards the future of probing smaller planets.