AGN ultra-fast outflows.

Over 2 decades ago X-ray observations first revealed the presence of blue-shifted iron $K$ absorption features in the spectra of nearby Active Galactic Nuclei. They indicate the presence of powerful ultra-fast outflows launched from the innermost regions of the accretions disk with velocities up to $0.3c$. Systematic studies then showed that these disk winds are present in $\sim 40$% of the nearby AGN and may be connected to the outflows that are seen on large scales in the host galaxies. Recently, tailored X-ray observational programs on the best examples of these disk winds are shedding more light on their nature and driving mechanisms. At the same time, we are increasing the sample of powerful disk winds with deep ALMA observations that will allow us to understand whether the disk winds have indeed an effect on the large-scale cold ISM. Here we shall review our recent results obtained thanks to XMM & NuSTAR observations on the prototypes of the most powerful disk winds focusing on the importance of variability studies.