This paper encloses a complete and explicit description of the derivations of the Lie algebra D(M) of all linear differential operators of a smooth manifold M , of its Lie subalgebra D 1 (M) of all linear first-order differential operators of M , and of the Poisson algebra S(M) = Pol(T * M) of all polynomial functions on T * M, the symbols of the operators in D(M). It turns out that, in terms o...