The present paper is focused on friction stir welding (FSW) of dissimilar aluminum alloys and steels, an area that is getting great concern recently. The promise of FSW joints lies in low welding heat input and its ability to minimize the extent of the formation of intermetallic compound (IMC) in dissimilar metals. The present paper assessed the status of FSW process of dissimilar aluminum alloys and steels, and to identify the opportunities and challenges for the future. The essential reason for the formation of the dissimilar Al/steel FSW joints with high quality is explained by super diffusion behavior. This paper will provide basis to designers and engineers to consider FSW for a wider range of dissimilar aluminum alloys and steels.