Heterogeneity represents a general feature of capillary networks. All of the parameters which describe hemodynamic, geometric or functional aspects of such networks exhibit considerable spatial dispersion. This is to some extent the result of the morphological and topological design of the network, reinforced by the nonhomogeneous nature of the flowing blood. Temporal dispersions are introduced by smooth muscle activity, which may be rhythmic or just oscillatory, but also by the passage of white cells causing transient perturbations. The functional relevance of perfusion heterogeneity follows from its effect on exchange efficiency. While evidence for the existence of physiological control mechanisms of heterogeneity is uncertain, intranetwork communication between upstream and downstream vessel segments appears to support the adaptation of supply to demand under physiological conditions.