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<jats:title>ABSTRACT</jats:title> <jats:p>We exploit the high sensitivity and moderate spectral resolution of the <jats:italic>Hubble Space Telescope</jats:italic> Cosmic Origins Spectrograph to detect far-ultraviolet (UV) spectral features of carbon monoxide (CO) present in the inner regions of protoplanetary disks for the first time. We present spectra of the classical T Tauri stars HN Tau, RECX-11, and V4046 Sgr, representative of a range of CO radiative processes. HN Tau shows CO bands in absorption against the accretion continuum. The CO absorption most likely arises in warm inner disk gas. We measure a CO column density and rotational excitation temperature of <jats:italic>N</jats:italic>(CO) = (2 ± 1) × 10<jats:sup>17</jats:sup> cm<jats:sup>−2</jats:sup> and <jats:italic>T</jats:italic> <jats:sub>rot</jats:sub>(CO) 500 ± 200 K for the absorbing gas. We also detect CO <jats:italic>A</jats:italic>–<jats:italic>X</jats:italic> band emission in RECX-11 and V4046 Sgr, excited by UV line photons, predominantly H <jats:sc>i</jats:sc> Lyα. All three objects show emission from CO bands at λ &gt; 1560 Å, which may be excited by a combination of UV photons and collisions with non-thermal electrons. In previous observations these emission processes were not accounted for due to blending with emission from the accretion shock, collisionally excited H<jats:sub>2</jats:sub>, and photo-excited H<jats:sub>2</jats:sub>, all of which appeared as a “continuum” whose components could not be separated. The CO emission spectrum is strongly dependent upon the shape of the incident stellar Lyα emission profile. We find CO parameters in the range: <jats:italic>N</jats:italic>(CO) ∼ 10<jats:sup>18</jats:sup>–10<jats:sup>19</jats:sup> cm<jats:sup>−2</jats:sup>, <jats:italic>T</jats:italic> <jats:sub>rot</jats:sub>(CO) ≳ 300 K for the Lyα-pumped emission. We combine these results with recent work on photo-excited and collisionally excited H<jats:sub>2</jats:sub> emission, concluding that the observations of UV-emitting CO and H<jats:sub>2</jats:sub> are consistent with a common spatial origin. We suggest that the CO/H<jats:sub>2</jats:sub> ratio (≡ <jats:italic>N</jats:italic>(CO)/<jats:italic>N</jats:italic>(H<jats:sub>2</jats:sub>)) in the inner disk is ∼1, a transition between the much lower interstellar value and the higher value observed in solar system comets today, a result that will require future observational and theoretical study to confirm.</jats:p>