Low-frequency QPO, Magnetic Flood and the states of GRS 1915+105

We sum up progress accomplished, since the last microquasar workshop, on the physics of the Accretion-Ejection Instability (AEI), and its ability to explain the properties of the low-frequency QPO of microquasars. These results concern the basic theory of the instability, its numerical simulation and the resulting modelisation of the QPO, as well as detailed observations of the QPO properties. They converge to reinforce the `magnetic flood' scenario, extrapolated from the AEI to explain the ~ 30 minutes cycles of G1915. We then discuss directions in which this scenario might be extended toward a more global view of the evolution of this source.