This document discusses the development of "cBooks", which are creative eBooks for mathematical thinking. The goal is to initiate a "Community of Interest" involving teachers from several European countries who can collaborate on designing cBook resources. CBooks act as "boundary objects" that facilitate crossing boundaries between different communities of practice. Factors like community size, integrating the work into normal jobs, and a sense of ownership over products can influence a community's efficiency. The document examines issues involved in building an international collaborative community around developing these types of mathematical resources.