A Tese examina o processo de criação e a forma final de filmes realizados por Jacques Rivette e John Cassavetes, entre 1968 e 1978, cuja invenção repousa numa poética da instabilidade. A partir de uma discussão mais abrangente das relações entre o método inaugurado pelos cineastas e a fronteira que ele instaura do cinema com outros campos, sobretudo o teatro, procedemos então às análises que confrontam dois pares de filmes: L\'Amour fou (Rivette, 1968) e A Woman Under The Influence (Cassavetes, 1974) e, em seguida, Out 1: noli me tangere (Rivette, 1970) e Opening Night (Cassavetes, 1978). Nesta abordagem comparativa, atentaremos para o modo pelo qual o estilo instável dos filmes prolonga, duplica e desdobra realidades dramatúrgicas igualmente instáveis, que eles tenderam a privilegiar. Para tanto, o estilo se deixa contaminar pelo happening, pela improvisação e pela teatralidade, radicalizando assim um impulso de experimentação permanente na obra de Rivette e Cassavetes, que lhe confere um lugar de destaque no cinema moderno. / This thesis examines both Jacques Rivette\'s and John Cassavetes\' creative processes, as well as the final cinematic forms of films they made between 1968 and 1978. The invention on their films rests on the poetics of instability. Starting from a more general discussion which examines the relationship between their original methods and the correlated connections they establish with other artistic fields, mainly the theater, we proceed to analyze the similarities and differences presented by two pairs of films: L\'Amour fou (Rivette, 1968) and A Woman Under The Influence (Cassavetes, 1974); Out 1: noli me tangere (Rivette, 1970) and Opening Night (Cassavetes, 1978). Through a comparative approach, we will observe the way the unstable style of films prolongs, duplicates, and equally unfolds unstable dramaturgical realities that they tended to privilege. In order to accomplish our task we will focus on the forms by which these films allow themselves to be contaminated by the \"happening\", by improvisation and by theatricality. Radicalizing their impulse of permanent experimentation, Rivette and Cassavetes managed to acquire a prominent position in modern cinema.