the work presented in this thesis is motivated by the need for new and effective methods to isolate vibrations in the rapidly growing technological sector, with particular interest in the control methodologies for active vibration isolation of a proposed isolator. the thesis consists of four major parts. the first part (chapter 2) focuses on the development of dynamic mathematical models for the isolator. the nonlinear force and stiffness models are linearized and a dynamic experimental characterization is conducted to properly identify the system parameters. the characterization also serves as a model validation process. the second part (chapter 3) investigates the ability of the active vibration isolator to perform with a phase compensation technique. this technique is realized by minimizing the 2nd norm of the displacement transmissibility. an automatic on/off tuning algorithm is devised to take full advantage ofboth active and passive modes. real-time experiments demonstrate the efficacy of the technique. the experimental results also show that with the proposed control scheme, the isolator is able to effectively suppress base excitations taking advantage ofboth active and passive modes.