Laboratory‐scale studies of discrete fractures lead to better understanding of the relationship between flow properties and pore geometry. Field‐scale studies of fracture networks test the validity of classical continuum approaches for transport processes in heterogeneous media. During 1987 to 1990, earth scientists have made significant advances in quantifying flow channeling and solute breakthrough in rough‐walled fractures, analyzing transitions between fracture and matrix flows under multiphase conditions, and characterizing fracture networks with hydrological and geophysical studies. In this review, the effect of heterogeneity and the issue of scaling are discussed. Many common features and similiar approaches can be identified in microcracks, discrete fractures, soil macropores, fractured rock masses, and heterogeneous reservoirs at different scales.