Title:MIDI Observations of the Young B Star MWC349A Abstract: We present observations of MWC349A with MIDI at the VLTI (the Mid-Infrared Interferometric Instrument at ESO''s Very Large Telescope Interferometer), which are a prime example of the power of combined spatial and spectral resolution for addressing complex astrophysical phenomena. Previous observations of the peculiar emission line star MWC349A suggest that it is a young massive star in the short-lived phase when the parental cloud has been completely dispersed, but the accretion disk has not yet been destroyed by ionization. The system is seen nearly edge-on; the unique hydrogen recombination line maser / laser activity of MWC349A from mm to infrared wavelengths is likely a consequence of this viewing geometry. We have taken 13 measurements with MIDI at the VLTI (Very Large Telescope Interferometer) in the GRISM mode covering the N band (8 to 13 microns) at a spectral resolution R~230. The wavelength dependence of the continuum visibility agrees with model calculations for circumstellar dust disks. In addition, the signatures of at least a dozen emission lines have been identified in the interferometric data. We present a first analysis of visibility amplitudes and differential phase data. In particular we show that a simple model can represent the SED and visibility amplitudes of the continuum flux. The visibilities for the hydrogen and forbidden lines are also discussed.