In the present book, we have dealt with theoretical investigations of some problems of Magnetohydrodynamics. The fluid has been assumed to be incompressible, electrically conducting and viscous or visco-elastic and the fluid motion is either steady or unsteady. Assuming the magnetic Reynolds number to be small, the induced electric and magnetic fields are neglected in some problems under the study. We discussed here seven important problems- Effect of Radiation on MHD Vertical Channel Flow, Laminar MHD Slip Flow past a Circular Cylinder, Unsteady Free Convection MHD Flow, Effects of Convection on MHD Coupled Flow Bounded by a Highly Porous Bed and Imperfectly Conducting Walls, Soret Effect in Generalized Couette Flow of a Binary Mixture of Electrically Conducting Fluids,2D Laminar MHD Boundary Layer Flow past a Wedge with Slip Velocity & Unsteady 2D Flow and Heat Transfer through an Elastico-viscous Liquid. This work will be invaluable to post-graduate students and researchers in applied physics, fluid mechanics, chemical and mechanical engineering.