Joining of dissimilar lightweight materials. Assembling multimaterial structures is challenging because of differences in melting temperature, formation of intermetallic compounds, differences in coefficient of thermal expansion, and galvanic corrosion potential. While the number of joining techniques continues to grow, for high-volume production, there is a continued desire for a single joining method that can assemble advanced high-strength steel, aluminum, magnesium, and composite materials, and combinations of some of these materials, consistently and robustly. This is especially crucial for the transportation sector, since it is one of the largest contributors to greenhouse gas emissions, especially in the United States. Even small reductions in weight can have a significant effect on the fuel consumption and emissions of the transportation sector. The cover shows an electron backscatter diffraction image of impact-welded silver (top) and copper (bottom), with colors representing the orientations of grains in the two materials and the interface; this is one of the techniques showing great promise for dissimilar materials joining. Image courtesy of Taeseon Lee and Taylor Dittrich of The Ohio State University. See the technical theme that begins on p. 608.