the electric point scattering theory that is well known as very effective means to describe random media, extraordinary transmission and plasmon particle arrays [@Lagendijk96; @Pedro98; @Abajo07]. In this paper we derive exactly such a theory for general magneto-electric scatterers. We show how reciprocity and energy conservation restrict the full magneto-electric response via Onsager constraints [@Landau; @Lindell_biisotropicbook], and a new magneto-electric optical theorem for the full polarizability tensor. This tensor not only includes an electric (magnetic) response to electric (magnetic) driving, but also off-diagonal coupling in which a magnetic (electric) response results from electric (magnetic) driving. While our theory sheds no light on the microscopic origin of the polarizability [@MerlinPNAS], we show how electrodynamic polarizability tensors can be directly constructed from LC circuit models. Furthermore we predict how extinction measurements and measurements of radiation patterns (i.e., differential scattering cross section) can be used to quantify the polarizability tensor.

The paper is structured in the following way: Firstly, in Section \[section:generaltheory\] we derive the general theory, taking into full account reciprocity, the optical theorem and radiation damping. In Section \[section:singleSRR\] we apply this theory to set up the polarizability of the archetypical metamaterial building block, a single SRR. In Section \[section:singleSRRexp\] we 