A review of theoretical and experimental investigations of laminar fluid now in porous ducts is presented. We extend the analysis of Terrill (1964) to derive similarity solutions for axial and lateral velocity profiles, pressure gradients and wall skin friction for the laminar, isothermal single phase now of incompressible fluids in channels having one or two porous boundaries. In contrast to previously published solutions, the approach developed here allows for any arbitrary value of suction or injection as well as non-zero slip velocities at the porous walls. It is found that whereas multiple similarity solutions can exist under certain conditions of suction, solutions obtained for injection are unique. Results from a finite difference solution to the vorticity-stream function formulation of the unsteady Navier-Stokes equations for flow in a porous channel are also reported and compared with previously reported perturbation, asymptotic, similarity and infinite series solutions.