  In the first part of this paper we outline the constructions and properties
of Fedosov star product and Berezin-Toeplitz star product. In the second part
we outline the basic ideas and recent developments on Yau-Tian-Donaldson
conjecture on the existence of K\"ahler metrics of constant scalar curvature.
In the third part of the paper we outline recent results of both authors, and
in particular show that the constant scalar curvature K\"ahler metric problem
and the study of deformation quantization meet at the notion of trace (density)
for star product. We formulate a cohomology formula for the invariant of
K-stability condition on K\"ahler metrics with constant Cahen-Gutt momentum.
