The aim of this chapter is to introduce a formal description for a knowledge system, by which to represent and connect the different epistemic states suggested by the previous theoretical analysis. The core of this description is the basic distinction between the epistemic notions of information and knowledge and the formalization of related states. The focal point is obviously the formal introduction of the notion of information, according to the basic principles described in Section 2class="EmphasisTypeItalic ">.6. On the basis of this description, a system of formal operations performed on different epistemic states is provided; they represent the actions of an agent on the informational contents towards the acquisition of new knowledge. The formal structure is that of Constructive Type Theory (CTT), introduced in Chapter 1.