Aerodynamics is the top-level of fluid mechanics science which is deals with the flow of air over bodies like aircraft or any other solid surface. Boundary layer can be classified into hydrodynamics and thermal boundary layer and had wide range of applications in the Aerodynamics. The present work examines the hydrodynamics boundary layer theory over a flat plate. It is interested subject due to its wide range of applications in industry and nature like airplane, missiles, rocket etc. the three laws of physics (mass, momentum and energy) had been derived and then the governing equations of boundary layer had been derivded. The boundary layer is sub-divided into three regions or zones, which they are the laminar, transition and turbulent boundary layer. The Integral Momentum Von-Karman Equation is derived in-full details over the flat plate and then it is used to derived the main parameters in the laminar and turbulent regions like rate of growth of each layer, skin friction coefficient, shear stress and drag coefficient. It is worthy to mention that despite various velocity profiles for laminar region, there is only one profile for the turbulent region which is the seventh root law that suggested by Prandtle. Also, for laminar boundary layer, Blasius proposed a solution that can be used to obtain the drag. The transition zone us discussed also and it is worthy to mention that the analysis of this region is limited in the textbooks of fluid flows and heat transfer.