Abstract: An apparatus for aligning the edges of a stack of sheets comprises a base and two plates mounted on the base for movement independently of one another. An oscillatory drive arrangement imparts oscillatory motion to the plates, the amplitude, frequency and orientation of the oscillatory movement being independently adjustable for each of the plates. A stack of sheets the edges of which are to be aligned is arranged on the plates so as to be supported on the plates on their support edges, and the oscillatory motion causes the individual sheets to move in a predetermined direction until the leading edges of the individual sheets reach an abutment preventing further movement of the sheets. A substantial volume of low-pressure air is blown between the individual sheets so as to separate them from one another and facilitate their independent movement toward the abutment. A pair of upright walls extends parallel to the direction of movement of the sheets so as to laterally support the stack.