  A (holomorphic) quantization of a complex contact manifold is a filtered
algebroid stack which is locally equivalent to the ring E of microdifferential
operators and which has trivial graded. The existence of a canonical
quantization has been proved by Kashiwara. In this paper we consider the
classification problem, showing that the above quantizations are classified by
the first cohomology group with values in a certain sheaf of homogeneous forms.
Secondly, we consider the problem of existence and classification for
quantizations given by algebras.
