The task of a Broker is to interpret relevant knowledge acquired by cognitive and perceptual psychologists and bring it suitably to the notice of interaction designers, thereby avoiding the need for that designer to have knowledge of cognition and perception. The task is first illustrated by an example based on the concept of Design Actions and demonstrates the implication, for two different design challenges, of certain properties of the human visual processing system. It is then argued that the task of the Broker can be eased by the definition and classification of relevant concepts, in the illustrative example those of browsing, interaction and visualization. Finally, a current need for a Broker’s expertise is illustrated in the context of the interactive and dynamic exploration of the relationships associated with a multivariable system.