This thesis presents a new passivity preserving model reduction method for circuit simulation, based on interpolation of dominant spectral zeros. Implemented as an eigenvalue approximation problem, the dominant spectral zero method (dominant SZM) is based on the subspace accelerated dominant pole algorithm (SADPA), which computes dominant spectral zeros automatically. The application of dominant SZM is extended beyond its interpolatory nature, proposing solutions for several problems in passive reduction. In particular, better approximation is achieved when combined with partial realization for descriptor systems, a framework for SISO reduction of the voltage transfer function in transmission lines is presented, and the implementation of MIMO dominant SZM is developed. Dominant SZM reduces automatically passive circuits irrespective of how the system equations are formulated, transmission line models with controlled sources, or circuits containing susceptance elements. Results show that dominant SZM gives comparable and often more accurate reduced models than state of the art techniques.