In foundation design, the serviceability limit state often is the governing criterion, particularly for large-diameter piles and shallow foundations. In addition, it is widely accepted that foundation movements are difficult to predict accurately. Most analytical attempts have met with only limited success, because they did not incorporate all of the important factors, such as the in-situ stress state, soil behavior, soil-foundation interface characteristics, and construction effects (Kulhawy, 1994). A survey of some of these analytical models showed that the uncertainties involved in applying each model and evaluating the input parameters were substantial (Callanan and Kulhawy, 1985). Ideally, the ultimate limit state (ULS) and the serviceability limit state (SLS) should be checked using the same reliability-based design (RBD) principle. The magnitude of uncertainties and the target reliability level for SLS are different from those of ULS, but these differences will be addressed, consistently and rigorously, using reliability-calibrated deformation factors (analog of resistance factors).