Design rules are directives that guide the design process towards the product. They are often specific descriptions of decisions and acts, which, taken as a whole, make up a design. Sometimes numeric, sometimes verbal, and most often visual or spatial, these descriptions have formed the core of analyses and recreations of design thinking since early history, with the most recent connotations arising in design computing. This issue of the Network Nexus Journal is dedicated to Lionel March, whose seminal contributions to computational art, architecture and design have profoundly influenced our understanding of creative thinking since the 1970s. As the preparations ensued for the tenth Nexus conference ‘‘Nexus 2014: Relationships between Architecture and Mathematics’’ (Ankara, 2014), it was decided that one of the sessions, Rule-Based Design, was to celebrate the legacy of Lionel March in the year of his 80th birthday. Four of the papers presented in that session in Ankara have found their way to this special issue. When Lionel could not attend the conference personally, Kim Williams and I pursued the idea of a celebration in other forms. I am grateful to Kim, who then invited me to guest edit this issue and gave me the chance to bring together texts by prominent scholars of computational design and architecture with much appreciation for Lionel’s presence in the field. In line with the breadth of the impact that Lionel March has had in the field, the issue offers fourteen texts on a variety of topics and approaches of research. Seven of the papers focus on design ontologies, typologies, generative specifications and generating designs that range in scale from the city to furniture. Nine of the papers, some overlapping with the above seven, either directly focus or refer to shape grammars, a computational theory of shapes and visual thinking in design. Among