A prototype can be generally defined as a preliminary version of a final product and it can represent both aesthetic and functional features. Prototyping, the process of building a prototype, constitutes an indispensable part of product development processes. Many classifications of prototypes which use a different range of criteria have already been developed and are known as Prototype Taxonomies. This paper proposes an agenda towards the development of a new taxonomic classification which will be based on a prototype's attributes and its intended purpose. This work is justified from the results of an analysis of 8 existing prototype taxonomies which indicate that there is not a taxonomy that explicitly uses the prototypes’ purposes as its basic taxonomic dimension. A definition of the term ‘Prototype Purpose’ is proposed through discussing the differences and relations to the term ‘Prototype Role’. This work results in a list of 23 explicit prototype purposes which arise from 7 roles of prototyping found in relevant literature: Learning, Communication, Demonstration, Integration, Refinement, Exploration and Requirement Elicitation.