Structural control technology has been widely accepted for the protection of structures against seismic hazards. Passive base isolation is one of structural control techniques that can be employed to enhance the performance of structures subjected to severe earthquake excitations. Isolation bearings employed at the base of structures naturally increase the structural flexibility, but concurrently result in large base displacements. The combination of base isolation with active control, i.e., an active base isolation, creates the possibility to achieve a balanced level of control performance in reductions of either floor accelerations or base displacements. Many theoretical papers have been written by researchers, on active base isolation for buildings and some experiments have been conducted for unidirectional excitations. However, earthquakes are intrinsically multi-dimensional, resulting in out of plane responses, including torsion responses of the structures. Hence, the focus of this paper is the development and experimental verification of active base isolation for buildings subjected to bi-directional seismic excitations. First, solutions to this control-orientated problem are given by a series of procedures in system identification using the proposed system identification procedure, control designs with considerations of realization based on the H2/LQG control algorithm, and methods to evaluate this control performance. Designed controllers for achieving balanced performance are validated on a six degree-of-freedom shake table in the Smart Structures Technology Laboratory at the University of Illinois at Urbana-Champaign.