Over the last few years there have been important efforts to improve the rigor, unity and operationality of Design theories. This work builds on the multiple (but scattered) theoretical proposals in recent decades: General Design Theory and Axiomatic Design in the 80s, Coupled Design Process in the 90s, Infused Design and C-K Theory in the 2000s. These theories echoed issues in practices (e.g., new design tools, innovative design) and the advancements of other sciences (e.g., artificial intelligence, set theory, engineering sciences). They contributed to ground a research community that has been reinvigorated by several initiatives. Parallel to this effort, design theory is being debated in other disciplines such as information systems, management studies and industrial design following the flourishing of design thinking in these areas. This special issue was launched to gain better understanding of the early efforts in design theory, as well as showcasing promising contemporary research in design theory.