This thesis deals with a specific class of musically improvised phenomenons : the one's that are produced by at least two musicians in simultaneous and open improvisation. Musicians in this situation face a specific challenge : the lack of common mmusical (or non-musical) set of imputs which can shape the formal process of the improvisation (horizontal indeterminacy) or assure the mutual coexistence of the improvised discourses (vertical indeterminacy).In the following, we postulate that collective free improvisation, as an interactive, strategic and collaborative situation, falls under the generic category of coordination problems.Having established this point, we consider the question from different perspectives. In the first part, game theory, or to be more precise, focal points theory, is used to determine the cognitive heuristics which help musicians in the coordination task. Then we show in the second part that the very idea of coordination is central to the formal dynamics of collective free improvisation. This theorical framework is finally completed by two kinds of empirical data : the analysis of Company Week's excerpts, a festival founded by guitarist Derek Bailey, in the third part ; and the results of five proto-experimentations conducted with musicians from both the Norwegian Academy and Lyon's CNSMD, in the fourth part.
