As opposed to the ADAFs described above, standard, radiatively-efficient accretion disks are optically-thick (i.e., opaque) across all frequencies of interest -- thus all of the radiation directly attributed to the accretion disk must be reprocessed through its outer layers. To be slightly more precise, we shall refer to the outer few Thomson depths8 of the accretion disk surface as the ``atmosphere''. It is obviously crucial to study the disk atmosphere if we are to use observations of accretion disks to study the environment of black holes. Due to the scope of this review, we focus on the reprocessing and ``reflection'' of X-rays by the disk atmosphere.