The aim of this article is to describe the minimum units of conversational structure. These minimum units, the Act and the Subact, take part in the segmentation of conversation in information units, that allow to recognize a hierarchical organization in our linguistic emissions. There are some segmental and suprasegmental marks that delimit the extent of Acts and, in the other hand, there are also several pragmatic functions that allow to see dicerent kinds of Subacts. In summary, Act and Subact are the first step to analyze the oral discourse and to set up the so-called Conversational Grammar.