Nominal dimensions may not be achievable during manufacturing processes, due to technological or financial limitations. Therefore, tolerance allocation is of significant importance for successful assembly. The information required to allocate tolerances for complex parts and assemblies is, however, generally not available at the initial design-stage. The research on tolerance synthesis has, therefore, been conducted to develop methods, algorithms and processes, with primary focus on manufacturing, assembly, cost and quality issues. In the reported research, a framework was proposed to compile available information for developing an integrated tolerance synthesis model and a step-by-step tolerance allocation process. Architecture of the model and the process would provide a foundation for the development of a tolerance synthesis software. The research has also been extended to explore the applications of FE simulation, as a virtual tool, to the prediction of the influence of geometric tolerances on the part distortions for complex part-forms and assembly design