In this paper, we introduce an analytic effective medium theory of plasmonic metamaterials founded on electrostatic eigenfunctions of plasmon states. The emphasis is on the sub-wavelength particles and metamaterials with unit cell much smaller than the optical wavelength. The theory covers plasmonic structures with arbitrary degree of symmetry: from completely asymmetric (including chiral) structures to fully isotropic ones. We also review several previously reported theoretical techniques used for calculating the effective parameters of plasmonic metamaterials in connection with our new theory. Several examples of negative permittivity and negative permeability plasmonic metamaterials are used to illustrate the theory.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.