This thesis, aimed at studying the complexity of the praxis system, is divided into two parts: First, a battery of tasks has been devised to assess each store of the current cognitive models of gesture production. Second, a series of tasks has been prepared to specifically study the action semantic system. The stimuli were always chosen after a series of pilot studies. A group of healthy controls were administered the tasks to gather norms. The assessment of the cognitive model of praxis processing in a group of left-brain damaged patients revealed two interesting patterns: 1)  A double dissociation between meaningful and meaningless gestures reproduction; 2)  A selective deficit in the production of pantomimes associated only with a deficit of working memory. These findings allowed us to refine the model in two ways: suggesting that the non-lexical route is engaged only in the imitation of meaningless gestures, and adding a working memory space needed to carry out pantomimes. The evaluation of the semantic system was carried out testing left and right-brain damaged patients.  The performance of two patients gave rise to two contrasting cognitive patterns. One patient presented with a deficit of matching objects by function (conceptual knowledge) coupled with spared ability to select novel tools (action semantic). The second patient failed the action semantic task yet performed normally in the conceptual knowledge task.  These results support the hypothesis that conceptual knowledge should be kept conceptually separate from action semantic.