Cosmic reionization, which took place in the first billion years after the Big Bang, was a major event in the cosmic history. This transformation of all neutral hydrogen to ionize was probably caused by the first stars, galaxies and quasars. However, a direct proof of which sources were dominant is still missing. Dr. Ivana Orlitová from the Institute of Astronomy of the CAS reviews results of the serach for ionizing sources in both distant and nearby Universe, and presents a recent discovery of starforming galaxies that show signs of strong ionizing activity. and Ivana Orlitová.