High energy propellants subjected to sufficiently high stresses and high stress rates will ignite and begin to release chemical energy. The ensuing response can vary from mild reaction to high order detonation. Considerable experimental and calculational effort has been spent over the past decade to understand, to predict, and to modify this response. It is our purpose here to review this work with emphasis on the more recent work. Particular emphasis will be given to experimental work using guns to impact flat plates on oriented propellant samples. Such experiments offer special advantages from both an experimentalist's and analyst's point of view because of accessibility of diagnostics and because of simpler geometry.