In this article, we review papers on precursors for the 2011 off the Pacific coast of Tohoku Earthquake. We discuss phenomena such as seismic, geodetic, electromagnetic, ionospheric, and macroscopic anomalies for which time scales range from a few decades to a few hours, from long-, mid- to short-term precursors. Of these, we treat ionospheric anomalies in the greatest detail. Through our review, we found that many "signals" preceded the 2011 off the Pacific coast of Tohoku Earthquake.