In this thesis, new analytical tools for performance evaluation of multiserver systems are developed. The new analytical tools allow us to analyze the performance of various resource allocation policies for multiserver systems for the first time. Our analysis leads to many insights and lessons that are useful, for system designers, in capacity planning and designing resource allocation policies for multiserver systems. In particular, our analysis shows a tremendous benefit of resource allocation policies with resource sharing or cycle stealing, when these resource allocation policies are designed carefully. Further, principles and guidelines are provided for designing these resource allocation policies.