Variability in Blazars

In this report, a review of historical observations and studies to the variability in blazars is given.The variability timescale, in particular, the optical variability timescale, is emphasized owing to its importance.Three samples of three different kinds of variations are presented, and the corresponding models to interpret them are given.The long periodic variability is paid a lot of attention because which could be explained by the eclipses of the binary supermassive black holes (SMBHs).In addition, the observed evidences, such as the periodic outbursts in OJ 287, supporting the binary SMBHs model are also presented.A brief conclusion and prospect is presented at the end of this report.