Summary: Kernelization is a polynomial-time algorithm that reduces an instance of a parameterized problem to a decision-equivalent instance, the kernel, whose size is bounded by a function of the parameter. In this paper we present meta-theorems that provide polynomial kernels for large classes of graph problems parameterized by a structural parameter of the input graph. Let \(\mathcal{C}\) be an arbitrary but fixed class of graphs of bounded rank-width (or, equivalently, of bounded clique-width). We define the \(\mathcal{C}\)-cover number of a graph to be the smallest number of modules its vertex set can be partitioned into, such that each module induces a subgraph that belongs to \(\mathcal{C}\). We show that each decision problem on graphs which is expressible in Monadic Second Order (MSO) logic has a polynomial kernel with a linear number of vertices when parameterized by the \(\mathcal{C}\)-cover number. We provide similar results for MSO expressible optimization and modulo-counting problems.