A three-dimensional fracture network in a granite block is reconstructed from a series of experimental serial sections. It is visualized and its most important geometrical characteristics are studied, namely the orientation of the fractures, the connectivity of the fractures, the number of cycles, per unit volume, the distributions of surface areas and of the intersection lengths, and the number of finite solid blocks isolated in the solid matrix by the network. Though the network mostly consists of two families of fractures, it is interesting to note that a simple model of randomly oriented, monodisperse hexagons often yields a good order of magnitude for the various geometrical properties, which have been measured on the real block. The flow properties are then studied; examples of velocity field are provided as well as histograms of velocities; the permeability tensor is determined and is found to be in good agreement with Snow's formula. Finally, dispersion is analyzed by means of a random walk method; histograms of arrival times are provided and interpreted in terms of dispersion tensor. ¿ 2000 American Geophysical Union