This article considers the nature of complexity and design, as well as relationships between the two, and suggests that design may have much potential as an approach to improving human performance in situations seen as complex. It is developed against two backgrounds. The first is a world view that derives from second order cybernetics and radical constructivism. What is particular about this view is that it accepts that our understanding of the world is made by us, regardless of whether it originates in an external reality or not. Indeed, it regards the question of whether an external reality can ever be known by us as essentially undecidable, which is part of its power. In terms of complexity, this leads to the position that we choose the complexity we see in the world. The second is design. Design is a way of behaving that approaches complexity in a different way (and expecting a different type of outcome) than we have conventionally used. Designers work in a way (a conversation with the self via the medium of drawing) that allows them to deal with very complex, ill-defined and ambiguous situations that would probably be inaccessible using conventional approaches. The outcomes of design are generally novel but can never be argued to be the best solution. Design is necessarily a constructivist, second order cybernetic activity. It is suggested that, as second order cybernetics and radical constructivism give us new insights into the nature of complexity, design gives us a way of acting that comprehends these insights.