This work takes the case of laurent schwartz (1915-2002) to study the collective life of mathematics in the second half of the 20th century.Its goal is to show how collective practices have then been constitutive of mathematical work and community, as well as how they evolved over this period. through a biographical lens, by considering schwartz both as an important actor who has left numerous traces and as a simple witness, we present several tableaus of the collective. we study the encounter between schwartz and the collective life of mathematics during world war ii, in particular through his interaction with the bourbaki group. we then analyze the diffusion of the theory of distributions in mathematics and its historiography, and show schwartz?active role in these processes. a chapter devoted to the kernel theorem (théorème des noyaux) and its later written incarnations allows us to deepen our study of interactions between writing practices in mathematics and various kinds of collectives. Three forms of collective organization of the mathematical work are then investigated: the conference (through a study of the 1947 colloquium on harmonic analysis), the seminar, and, finally, the mathematical research center (taking as an example the centre de mathématiques de l'ecole polytechnique). Finally, we take on the question of schwartz's political engagement as a mathematician. we wish to show how this engagement embodies a certain conception of the mathematical community, while taking some inspiration from its particular social practices