Published online by Cambridge University Press: 04 August 2017
We have to date reports of Quasi-Periodic-Oscillation (QPO) observations in some twelve X-ray source, of which at least seven are low mass X-ray binaries (van der Klis 1987). They constitute a formidable zoo of phenomenae with so much variety that they, at times, do not at all even seem amenable to a single model. Some of the other QPO talks in these proceedings will try and present observations in the context of various models. My task is to talk about the Beat Frequency Model which, it seems to me, is by far the prime model for at least some of the QPOs.