The present article tackles the issue of the unity and cohesion of the world as it is evoked by Lucretius in the De Rerum Natura. Through this work, we would like to show that the philosopher offers an original solution to this question by using a biological model: the organic unity. This model plays a dual role, both critical and descriptive. First, it replaces what Lucretius identifies as ‘false models’ of the union and cohesion of the world: the model of the world as living based on the theory of the soul of the world, the model of the world as divine, rested on demiurgic and providential theories and finally the model of the world as principle, elaborated from the thesis of the eternity of the world and its parts. Then, by evicting these three models of explanation and description of the cohesion of the parts of the world, based on a bad definition of the nature of the world, the Lucretian biological model proposes a re-description of the unity of the world which is compatible with the Epicurean cosmological theses of the plurality of worlds and of the mortality of the world.