Much has been learned about exoplanet atmospheres in recent years. For transiting extrasolar planets, transmission spectroscopy -- measurements of the spectrum of stellar light transmitted through the planetary atmosphere during transit -- has been a valuable tool for constraining atmospheric properties. To date, transmission spectroscopy has been used as a tool for constraining atmospheric composition, cloud structure, hazes, and winds in a variety of exoplanetary atmospheres. In this talk I will focus on recent modeling and observational results that have pushed the capabilities of this method. The first is the use of transmission spectra to constrain the atmospheric properties of the transiting super-Earth GJ 1214b. The second is the use of Doppler shifted transmission spectra to measure wind speeds in tidally locked hot Jupiters.