On the 11th of February 2016, the LIGO scientific collaboration and Virgo announced the first direct detection of gravitational waves, marvelling the scientific communities and sparkling a huge interest on the media and the general public. On the 16th of October 2017 we did it again. This time together with 70 observatories of EM radiation, we announced the observation of the collision of a binary system of neutron stars, giving rise to the dawn of multi-messenger astrophysics. Measuring the impossible, as Einstein predicted, has been a long and difficult journey, that started a century ago with the prediction of the existence of gravitational waves. The scientific importance and technological achievement that made possible the detection of gravitational waves has recently been awarded with the 2017 Nobel Prize in Physics. As a member of the LIGO Scientific Collaboration (LSC) is a great pleasure to be able to talk to you about this fascinating subject. In this seminar, I will introduce the concept of gravitational waves before describing the first detection (GW150914) of a signal generated 1.3 billion years ago during the merger of two back holes. I will also talk about the last announced detection of the signal generated during the merger of two neutron stars. We will look into the astrophysical implications of both detections and finish with the description of the detectors and their technology.