The recent historical detection of gravitational signals by LIGO has drawn attention to the huge amount of work which has been needed for obtaining, after more than thirty years of technological efforts, this breaking result. Moreover, enhancement of the sensitivity of the existing detectors as well as plans for future instruments is likely to attract new scientists, so that it seems useful to recall the background of this field of research. Obviously we will present the state-of-the-art in operating detectors. It is also likely, after the success of LISA Pathfinder ([2]) that spaceborne detectors will trigger a larger interest, and that the very long wavelength band will be explored in the coming decades.