In this talk we will present a new zonal wavefront sensor. The device consists of a multiplexed hologram which can reconstruct multiple diffracted beams to an image plane with the input of a single object beam. In operation, a wavefront incident on the hologram is divided up into various output beams according to the presence and strength of particular aberrations present in the input. The Zernike terms are then simply read out according to the location of the foci on the image plane CCD. The wavefront information is thus derived without the need for any computations; in effect representing an all-optical, massively parallel processing method with virtually limitless bandwidth. Furthermore, because of the minimal computing electronics required this type of sensor is compact and permits active wavefront sensing for very small imaging devices.