To present an overview of the numbers and types of human embryos used in research projects in Belgium from 2007 to2015. Analysis of all research proposals approved by the Federal Commission for Medical and Scientific Research on Embryos InVitro. Not applicable. Not applicable. Number of embryos used for research, number of embryos created for research, and areas of embryo research. Since 2007, 15,811 embryos were used for 36 research projects. In total, 10,492 (66%) fresh supernumerary embryos (unfit for transfer or freezing) were used, 4,083 (26%) frozen supernumerary embryos (donated by parents whose child wish was completed or abandoned), and 1,236 (8%) embryos created for research. Most projects focused on research into embryo development. Fresh supernumerary embryos were mainly used for human embryonic stem cell (hESC) research. Frozen supernumerary embryos were almost exclusively used for research into embryo development and for hESC research. Embryos created for research were used for research into embryo development, oocyte research, research into cryopreservation of oocytes, and hESC research. Having concrete data on embryo research is crucial for an informed debate. Moreover, these data are necessary to find out trends in research such as the numbers of embryos needed and the areas of research. Data collection requires a sufficiently clear definition of "research" and "embryo." These conceptual questions frequently reveal lack of clarity in legislation.