I present an observational and theoretical study of high-amplitude delta Scuti stars. In the observational part of this dissertation, I quantify the pulsation behavior of the 90 MACHO delta Scuti stars and compare their pulsation properties to those of other known high-amplitude delta Scuti stars. The pulsation behavior of the MACHO delta Scuti stars are found to be similar to those of the field high-amplitude delta Scuti stars, although there are significant differences between the field, MACHO, and OGLE samples as a whole because of observational biases. The MACHO delta Scuti stars significantly increase the number of known high-amplitude delta Scuti stars. In the theoretical part, I use stellar evolution and pulsation codes tested on other pulsating variables to study the radially-pulsating delta Scuti and SX Phoenicis variables. I describe a grid of stellar evolution models with a range of masses and element abundances consistent with those of observed delta Scuti stars, which I then test for pulsations using both linear and non-linear pulsation models. The evolution and linear pulsation models are found to produce similar results to other recent modeling work using up-to-date opacity and equation of state data. These pulsation models also match observed double-mode delta Scuti stars whose masses, temperatures, and element abundances are known. The non-linear models produce self-sustaining pulsations of delta Scuti models, although the amplitudes and light curve morphologies of the models are different from observed stars. Reasons for these differences are discussed as well as possible areas of improvement.
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