Friction stir welding is a novel joining process extensively used for welding of aluminum alloys. It is widely known that the process parameters involved in friction stir welding play a pivotal role in determining the final characteristics and microstructure of the joint. However, it is still unclear that what combination of process parameter values will lead to the optimum joint characteristics. Taguchi technique is a handy and efficient method that has been widely used for performing optimization in manufacturing engineering. In this paper, lap joint friction stir welding was performed on AA1100 and the process parameters were optimized using Taguchi L16 orthogonal design of experiments. Unlike previous studies on optimization of friction stir welding process in aluminum alloys, a more comprehensive approach has been taken towards the number of input and output parameters of the process. Process parameters considered in this study were tool rotational speed, tool traverse speed, tool tilt angle, and tool pin shape. The optimum design was obtained with reference to output parameters including hardness and grain size in the weld center zone, maximum working temperature, joint tensile strength, and elongation as well as the vertical and horizontal forces on the tool during the process. Analysis of variance was additionally performed to evaluate the significance of each design parameter on output parameters. Results gained from analysis of variance indicated that rotational speed and traverse speed were the most critical parameters in determining the weld mechanical properties as well as quality of the weld microstructure. Finally, to validate predicted optimum values based on Taguchi technique, confirmation tests were conducted, where an excellent agreement was observed between the predicted and experimental values, showing accuracy of the employed method and obtained results.