Experimental observations suggest that toroidal plasma rotation can play a crucial role in determining the stability of a tokamak. Conventional MHD stability analysis ignores rotation. Results from analytic and numerical analysis of a number of tokamak stability issues including toroidal plasma rotation are reported. Depending on the plasma and rotation profiles, the net effect of rotation can be either stabilizing or destabilizing; it also has a substantial effect on the observed mode structure. Localized interchange, the double kink mode, low-n resistive MHD modes and the effect of sheared rotation on magnetic island structure are discussed.