Non-Newtonian third grade fluids find application in many areas such as geophysics, chemical and nuclear industries, oil reservoir engineering, and many others. The negative effects of magnetic forces is a problem to the fluid's flow. Also, the methods of solution employed sometimes do not give the actual physical behaviour of the fluid. Therefore, in this book we investigated the flow of a third grade fluid through a cylindrical pipe in the presence of magnetic field and joule heating and the Adomian decomposition method was applied to the model equations for the Reynolds' viscosity model case. Graphs depicting the velocity and temperature distributions for various values of the thermo-physical parameters were presented, from which we observed that the magnetic effect parameter decreases the velocity of the fluid and increases the temperature while the joule heating parameter reverses the effect of the heat generation parameter. This book has been written for the benefit of undergraduate and postgraduate students in the mathematical sciences; physics and engineering as well as researchers in the areas of fluid dynamics, differential equations and mathematical modelling.