Vibration-sensitive equipment within buildings may be susceptible to damage from harsh floor motions transmitted from the primary structure due to strong ground motions. Isolation devices are capable protecting fragile equipment from seismic hazards by decoupling individual pieces of equipment or entire floor slabs. A practical limitation associated with equipment isolation is that these systems have limited displacement capacity, which if exceeded lead to impacts degrading performance. However, even the most e ective isolation systems are incapable of protecting equipment from building collapse. This study investigates the use of floor isolation systems (FISs) as multi-functional structural units to mitigate both equipment accelerations and structure responses to achieve desired building-system performance. These multi-functional FISs not only serve their traditional purpose (equipment isolation), but they are also engaged to protect the primary structure under extreme earthquake loads by passively adapting to function as nonlinear dynamic vibration absorbers. In so doing, this concept bridges the gap between equipment isolation and vibration absorption, yielding a novel adaptive passive seismic protective technique. Simulation results indicate that multi-functional FIS can reduce equipment accelerations for small to moderate earthquakes, as well as deflections (drifts) of the primary building over a range of disturbance intensities. Overall, multi-functional FISs are shown to enhance building-system resilience over a broad range of seismic hazard levels.