Abstract
In this paper I review progress made in the last few years in explaining the low-frequency QPO of microquasars by the Accretion-Ejection Instability, and how this may guide us in understanding the short and long term variability of these sources. I then turn to another, closely related instability, which also relates to diskoseismologic models. I show how it might apply to explain the high-frequency QPO of microquasars, and the flares in Sgr A*, the massive black hole at the Galactic Center.
