In this book, a quasi steady state model for mucus transport in airways under time dependent pressure gradient, caused by mild forced expiration, is proposed and analyzed.It is assumed that while air blows under mild turbulent conditions, the adjacent mucus layer flows under unsteady laminar conditions. Effect of slip caused either by immotile cilia bed saturated with serous fluid in large airways or surfactant at the wall surface in smaller airways, on mucus transport is also considered in the model.