© 1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. This paper describes a passive damping program for fan and compressor blisks. Specific goals include the design, manufacture and spin test of two passive damping systems to achieve effective magnification factors (Q) of 50 or less for the targeted modes of vibration. The two selected damping systems are a viscoelastic constrained layer design and a dry particle damping design. Emphasis is placed on developing damping systems which are as production-ready as possible. They must be effective and reliable under the static loads, the dynamic loads, and the temperature extremes produced in real turbine engine environments. To these ends the designs are being driven by practical manufacturing and durability considerations. The design of the viscoelastic system is complete and fabrication is in process. Conceptual designs of dry particle damping systems are complete and a flat plate spin test effort is in process. Design analysis and limited bench test results show that Q's near 50 are achievable for both damping systems.