We prove that rigid cohomology can be computed as the cohomology of a site analogous to the crystalline site. Berthelot designed rigid cohomology as a common generalization of crystalline and Monsky-Washnitzer cohomology. Unfortunately, unlike the former, the functoriality of the theory is not built-in. We defined the "overconvergent site" which is functorially attached to an algebraic variety. We prove that the category of modules of finite presentation on this ringed site is equivalent to the category of overconvergent isocrystals on the variety. We also prove that their cohomology coincides.
