This book describes the advanced stability theories for magnetically confined fusion plasmas, especially in tokamaks. As the fusion plasma sciences advance, the gap between the textbooks and cutting-edge researches gradually develops. This book fills in this gap. It focuses on the advanced topics such as the spectrum of magnetohydrodynamics in tokamaks, the interchange modes, ballooning modes, and toroidal Alfvén eigenmodes, etc in the toroidal geometry. The theories are laid out in parallel with the ideal, resistive magnetohydrodynamics and gyrokinetics formalisms.