In preparation for the Large Synoptic Survey Telescope (LSST), which will revolutionize time-domain astronomy, it is critical that we understand variable phenomena as deeply as possible. Variability is arguably the defining feature of Active Galactic Nuclei (AGN), and is observed in every waveband, so variability studies are fundamental to understanding the extreme physical conditions of accretion disks near supermassive black holes. Several efforts have analyzed variability in the optical, however, to relate the variability and physical properties of AGN, we need well sampled light curves, which are still rare. At the same time very little is known about variability in the near infrared (NIR). At low redshift this waveband gives us information about the dust surrounding the accretion disk; at high redshift it tells us about the accretion disk itself. In this talk I will present our statistical analysis of the connection between AGN variability and physical properties of the central SMBH, where we found that the amplitude of the variability depends solely on the rest frame emission wavelength and the Eddington ratio. Besides, I will present some preliminary results of our Dust Reverberation Mapping analysis, where we are using NIR and optical light curves of ~100 type 1 QSO, with redshifts bellow 1.2, to study whether the emission received in the NIR is consistent with emission from a dusty torus, a wind or the accretion disk, and to determine the characteristic optical-NIR time lags, to study the different sizes of the AGN structures. Finally, I will present our results on variability-based AGN selection. We have selected AGNs candidates in the more problematic region of the colour-colour parameter space, where high-redshift AGN resemble stars.