Friction Stir Welding (FSW), a solid- state joining process, was invented at TWI in 1991. Although conventional FSW process may produce defect-free welds with reasonable properties of the weld regions compared with fusion welding process, the produced thermal cycle might be sufficient to reduce the mechanical and corrosion properties of the weld. Using the dual- rotation speed friction stir welding (DRS-FSW) where the pin and the shoulder are rotated at different speeds, the rate of input energy into the weld zone can be controlled. Although decreasing the maximum produced temperature within the weld zone using DRS-FSW has been reported; to the best knowledge of the authors; there is no published research on the individual effect of the pin or the shoulder rotation speed on the stirring condition inside the weld zone. Implementing differential rotation speeds of the pin and shoulder for friction stir welding process is considered. A model based on energy for predicting maximum temperature in conventional friction stir welding has been extended to estimate the heat evolution in the weld zone for dual- rotation speed friction stir process. The model predicts the relationships between the maximum temperature and effective process parameters including of pin and shoulder rotation speeds, and welding speed. The model suggests that the maximum predicted temperature is more responsive to change in the shoulder rotation speed than the pin rotation speed. The model has been verified using the data found in the literature and performed experiments. Experimental has been carried out using a designed and fabricated apparatus for dual-rotation speed friction stir welding. Metallographic studies of the welded samples reveal that individual proper selection of the pin and the shoulder rotation speeds not only results in obtaining defect free joints, but also affecting the weld zone via controlling the delivered heat input to the weld. This study also presents a novel approach for fabricating thin welded plates with excellent surface finishing and physical properties using friction stir welding process. Similar and dissimilar materials were welded under various conditions, followed by cold-rolling operations to the desired thin thicknesses. For similar welds, an ultimate thickness of 70micron was achieved from 1mm raw aluminum alloy 1100. In the next stage, where 0.5mm aluminum sheets were welded to copper samples with the same thicknesses, bi-material foils with final thickness of 200micron were fabricated. Results indicate that the presented approach can be replaced with costly fusion processes especially for ultra-thin joints. For further studies, it is suggested that some aluminum alloys is used for dual-rotation speed friction stir welding experiments. Keywords: Friction, Stir, Welding, Thermal, Model, Dual, Rotation, Speed, Shoulder, Pin, Aluminum.