The adaptation of bone to its mechanical demands is often described as a feedback control system wherein some aspect of the tissue strain environment acts as a driving signal to initiate cellular-level formation and resorption processes on bone surfaces. While this description may be somewhat simplified, the control system view is useful for organizing ideas, experiments, and simulations of adaptation. In the past 25 years, several investigators have introduced mathematical models and (finite element-based) computer simulations of bone adaptation, using numerous candidate driving mechanical signals as proposed bone mass regulators . These simulations generally use the finite element method — including the appropriate geometry, material description, and loading — to calculate the needed tissue strain parameter being considered as the specific regulation signal. Based on the adaptive response being simulated — geometric and/or material property changes — the finite element model is updated, and re-analyzed in a series of discrete time steps.