  We present here the main characteristics of the BHC IGR J17091-3624 outbursts
occurred several times since 1994. Since 2003, the source has been extensively
observed by INTEGRAL and Swift. In particular, we report results on the last
2011 outburst that showed a rare variability behaviour observed before only in
the galactic BH GRS 1915+105 but at a different level of flux. Several
hypotheses have been proposed in order to explain this particular behaviour.
They are all discussed here, in the light of their apparent contradiction.
Finally, based on all available informations, we attempt to give an overall
view of this enigmatic source and we speculate on the evolutionary state of the
binary system.
