these issues (and other possible sub-issues) in different ways. We will present and weave different threads over the different sections of this chapter, considering the different topics involved, their interaction, and the theoretical and methodological issues and approaches. In particular, we will look at tools and resources not as static products, but as evolving objects, which can be the products of teachers' collaboration, and can support and mediate collaboration. Since tools/resources are seen in this chapter as two sides (means and products) of a coin, using and designing them are then to be considered as two possibly interrelated processes. In the presentation of the glossary (Sect. 5.2.4), we will describe the shared meaning of the terms used in this chapter.