Chapter 1 introduces the empirical domain (interactional language) as well as the Interactional Spine Hypothesis and broadly situates it within the state of the art. It is shown that for the calculation of utterance interpretation, propositional meaning is not sufficient. Rather it is important to take the speaker’s intention into consideration as well as the addressee’s knowledge state. This sets the stage for the development of the interactional spine throughout the monograph.