SUMMARYAs a flrst step towards fonnulating guidelines for the design of dynamically reliable MEMS, we analyze the nature of the mechanical responses of shock-loaded microsystems. MEMS are modeled as microstructures supported on elastic substrates, and the shock loads are represented as pulses of acceleration applied by the package on the substrate over a flnite time duration. For typical MEMS and shock loads, the response of the substrate is closely approximated by rigid-body motion. Time-domain criteria, obtained to distinguish between the impulse, resonant, and quasi-static responses of the microstructures, correlate well with the experimentally observed behavior of shock-loaded MEMS.