There is widespread recognition of the scarcity of reliable data and research on Child Sexual Abuse Material (CSAM) and Child Sexual Exploitation Material (CSEM). This is due to the clandestine and criminal nature of these phenomena. As noted below, some studies documenting the use of technologies to sexually exploit and abuse children have been conducted, with an emphasis on the characteristics of those victims depicted in the imagery (e.g. Baartz, 2008; Canadian Centre for Child Protection, 2016; Carr, 2004; Quayle & Jones, 2011; Seto, Buckman, Dwyer & Quayle, 2018). However, the underlying constraints on evidence generation in the area remain. These are due, in part, to a lack of comprehensive and consistent data (e.g. on victim experience), methodological, ethical and legal challenges in researching CSAM/CSEM, and highly limited resourcing in relation to the significance of the issue. No representative international baselines of empirical data have been produced on the victimisation of children depicted in this material, or on the quality of the response by law enforcement agencies around the world to this problem. Through their respective programmes of work, INTERPOL and ECPAT International recognise an urgent need to fill this gap, in order to provide evidence to drive awareness-raising, to support advocacy for improved policies, laws and resourcing, to strengthen programming, and to enhance law enforcement and other intervention in the sphere of victim identification on an international level. The present study is intended as an initial effort towards this purpose, taking advantage of the momentum of heightened international attention and new commitments and partnerships for addressing OCSE, and the sexual exploitation of children more generally.BACKGROUND TO THE PROJECTThe idea of developing a global indicator for Child Sexual Abuse Material was first discussed by ECPAT and INTERPOL in 2015 in direct response to several calls in 2014 for increased research and indicators on this phenomenon. Those calls included the report of the Special Rapporteur on the sale of children, child prostitution and child pornography to the Human Rights Council, and the First #WePROTECT Children Online Global Summit.The production of a global indicator is also closely aligned with both the ECPAT International Strategic Framework 2015 – 2018 and Beyond (ECPAT International, 2016) and INTERPOL General Assembly Resolution AG-2011-RES-08 relating to “Promoting victim-centric management of child abuse material at the national level” (Interpol, 2011) , which was adopted unanimously by INTERPOL Member States in 2011. Both partners see research and measurement of OCSE as essential for understanding the scale and nature of the problem, and for designing appropriate responses and countermeasures.