The design of tools for creative activities affects the creative processes and output of users. In this paper we consider how an understanding of creative interaction can inform the design of support tools in a creative domain, and where creative needs cross domain boundaries. Using observations of musical composers we analyse the theoretical approaches to understanding creativity and their use to HCI. Cycles of ideation and evaluation are suggested as atomic elements of creative interactions, with the representation of ideas a central activity for individual and collaborating composers. A model of collaborative composition was developed, along with an analysis of the representational types used in the domain. This led to the design and evaluation of a prototype Sonic Sketchpad for musical idea representation. Author Keywords Creativity, Collaboration, Representation, Music, Composition. ACM Classification Keywords H5.m. Information interfaces and presentation (e.g., HCI): Miscellaneo...