The composition and spatial distribution of molecular gas in the inner few AU of young (< 10 Myr) circumstellar disks are important components to our understanding of the formation of planetary systems. In the first part of this talk, I will discuss the current, observationally-based picture of protoplanetary gas disks at r < 10 AU.  I will review the most widely used spectral diagnostics of the inner disk, and highlight recent observations of H2 and CO made by the Hubble Space Telescope.  I will describe how high-resolution spectroscopy is being used to constrain the composition, distribution, and evolution of molecular gas in the inner disk at spatial scales too small to resolve with current imaging instruments/facilities. In the second part of this talk, I will discuss how the spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres.  I will present results from a Hubble Treasury program that is currently underway to characterize the panchromatic (X-ray through mid-IR) radiation environments around low-mass host stars for the first time.  We find that all exoplanet host stars observed to date exhibit significant levels of UV/X-ray activity, and that strong flares are common, even on "optically inactive" M dwarfs hosting planetary systems.  I will briefly discuss the use of these data in atmospheric models of rocky planets around cool stars, including the predicted abiotic production of O2 and O3 - a cautionary tale for the interpretation of "biomarker" gases when they are detected in the coming decades.