Final Report Summary - HETRANSIENTS (Innovative tools for the study of high-energy transients) The Career Integration Grant has helped to create the High Energy Transients and their Hosts (HETH) group at the Instituto de Astrofísica de Andalucía, member of the Consejo Superior de Investigaciones Científicas (IAA-CSIC). The scientific research during the length of this project has been aimed towards the study of cosmic stellar explosions and the galaxies in which they die. This has resulted in 23 papers published in international refereed journals, as well as over 60 astronomical circulars.Highlights of the scientific research are: (1) The first spectroscopy of a short gamma-ray burst, which happens when two neutron stars end their lives in a violent merger. (2) The discovery and analysis of the first supernova associated to a hyper-energetic gamma-ray burst, by which we determined that these explosions have similar properties as the nearby faint events that had been studied before. (3) By studying the host galaxies of the newly discovered superluminous supernovae, we discovered that they are the first stellar explosions that happen in a star formation burst, even earlier than gamma-ray burst. This indicates that the progenitors of these explosions are extremely massive stars. (4) Through the study of large spectroscopic samples of gamma-ray bursts, we analysed the properties of the galaxy environments across the history of the Universe and observed the evolution of the metallicity (proportion of heavy elements in galaxy environments) since the formation of the first stars. (5) Finally, through the use of 3D-spectroscopy and tuneable filters, we are playing an important role in the resolved study of the galaxies of stellar explosions.Part of this research work has been supported and enhanced by the construction of a publicly accessible and collaborative database of spectroscopic observations of gamma-ray bursts (http://grbspec.iaa.es/). This currently includes the largest public collection of gamma-ray burst spectra available, as well as a suite of online tools for the visualisation and analysis of the data. This allows the users to perform research-grade studies online, without the need to download large amounts of data.During this period and thanks to the support of the MC-CIG grant, we organised the “Galaxies Meet GRBs at Cabo de Gata” international conference, in which we had 50 participants coming from 13 different countries. We also hosted in March 2014 a workshop of the X-shooter GRB group, in which 25 people of our international collaboration took part.Our scientific results were also disseminated through outreach activities, amongst which we can highlight: two events of “Ciencia en la Calle” (Science in the Streets; 14th and 21st September 2013), a public outreach talk and observing night (24th September 2013) during the Galaxies Meet GRBs at Cabo de Gata conference (27th September 2013), and a public outreach event as part of the “Researchers Night” (26th September 2014).