The marine controlled-source electromagnetic (CSEM) method for finding hydrocarbons was introduced in the 1980s but only found commercial acceptance about five years ago. However, this brief time has been long enough for this method to earn the label of being possibly the most significant technology in oil exploration since 3D seismic. Indeed, the field has grown so rapidly that it will be the subject of simultaneously published special sections in both SEG journals—perhaps an unprecedented occurrence. The March-April issue of Geophysics will have 10 peer-reviewed papers on CSEM. TLE's special section presents several case studies that show the value of the technology in reducing risk for exploration and development projects. Most CSEM surveys are marine but CSEM is also done on land, mainly in Russia and China. Marine CSEM is mostly done in the frequency domain; land activities are split between frequency domain and time domain.