This is an interpretative review article which does not attempt to cover the entire literature but an attempt has been made to discuss the important topics from an extensive array of literature data. The first half of this paper takes into account the effect of solid packings on the flow pattern of the fluid passing through a packed bed reactor. Fluid flow characteristics, velocity. profiles in the bed, within the packing voids and In the wall region. Since radial dispersion tends to create plug flow conditions, hence only axial dispersion, its mechanisms, effects of system variables on axial dispersion and wall and end effects have been discussed in the second half.