This paper concerns the informational requirements of layered manufacturing (LM). The most common industrial use of LM today is for rapid prototyping, but we take a wider view of it as a flexible fabrication technology. Its use in building functional metallic parts, layer by layer, under computer control has already been demonstrated in the research context, and commericial LM machines for bu9ilding productionparts are in prospect. We report ona study of current and proposed data formats for communication between the various stages of the LM process. They are compared, and attention is given to the issue of their extensibility to meet future needs. In this last respect, particular e3mphasis is given to materials-related and other non-geometric information needed for fabricating multi-material objects and objecxts with graded material properties. ONe conclusion is that the best way forwared is the creation of a new Application Protocol for the international standard STEP (ISO 10303), specifically to handle layered manufacturing information.