A summary of general considerations in active vibration isolation obtained from experience in developing a testbed system is given. Application of this approach is illustrated by a description of the testing facility and the results achieved to date. These include broadband active vibration isolation of 20 dB over a decade-wide frequency band on the nearly-full-scale testbed. Significant features of the testing facility are a small diesel engine mounted on a representatively complex structural foundation, the correspondingly complex open-loop transfer function of the system, and the use of a hybrid analog/digital controller to partition the compensation filter frequency coverage.