Beginning during the last decades of the twentieth century Research Ethics Committees (RECs) have spread to many regions of the world. The initiative to set up those committees is linked to an analysis of ethical aspects in medical research projects as published in an American medical journal of high reputation. The results prompted the National Institutes of Health (NIH) to require an assessment of research projects by an Institutional Review Board (IRB) as condition for granting that research. Authorities of other States followed this example. The World Medical Association by revising its Declaration of Helsinki in Tokyo (1975) introduced the obligation for physicians to present research projects before starting to an independent committee for ‘consideration, comment and guidance’. RECs feel responsible for the protection of human rights and fundamental freedoms of research participants. In accordance with national legislation they may work as kind of an authority or as an advisory board. More and more national and/or international legally binding instruments give the frame for decisions to be taken by RECs. International Guidelines of Non Governmental Organisations may assist the RECs in their decision finding.