Abstract : Contents: The occurrence of combustion instability in solid propellant rocket motors; The morphology of combustion oscillations; Theories of elemental processes in combustion instability - a literature survey; A detailed discussion of pressure coupling with the surface flame zone; Experimental studies on the nature of the pressure - surface flame coupling; Consideration of possible experiments to measure acoustic admittance; Acoustic admittance and entropy waves; Experimental apparatus; Experimental results; Damping mechanism studies; Conclusions and future experiments.