Stars evolve from their births to their deaths by converting their store of hydrogen to helium, and then much of this helium is fused to heavier elements such as carbon, oxygen, and up to iron. During this evolution, the stellar mass may decrease by a stellar wind mass loss, the radius usually greatly increases, and the radiation luminosity emitted at the surface grows until the stellar death results in a very small compact object. During this evolution, there are often several stages when the structure of a star is unstable against pulsations. These pulsations are observable and indicators of the internal details of its structure. Six of these self-excitation mechanisms, which produce limited amplitude pulsations, will be discussed and demonstrated. Three deep-seated ones are the modulated nuclear fusion reactions at the stellar centers, the possible Kelvin-Helmholtz instability at the surface of a rapidly rotating core of the star, and oscillation of convective eddies which has a restoring force due to a composition gradient in deep layers. Three mechanisms which operate in tbe outer layers are the oscillations of convective eddies restrained by a strong magnetic field, and the thermodynamic effects of blocking and hiding of the radiation luminosity due to the ionization of the abundant elements, hydrogen and helium.