Building the evidence base A prerequisite for action A pickup truck filled with Afghans leaving for neighbouring Iran makes its way through the rough Nimrozi landscape. Civilians trying to escape the insecurity in Afghanistan are paying smugglers to take them all the way to Europe. Photo: NRC/ Jim Huylebroek, August 2016 66 GRID 2017 A concerted effort is required to advance our understanding of the dynamics of internal and cross-border displacement, returns and onward movements and the relationships between them. A number of questions need to be answered if national governments, policymakers and humanitarian agencies are to meet the needs of all forcibly displaced people, regardless of whether they flee within or across borders. Such an evidence base is also a prerequisite for reducing the risk of new, onward and repeated displacement in future. First, we need to get better at capturing how many IDPs cross borders, and where and when this happens. What proportion of refugees, asylum seekers and migrants were previously IDPs, and how does this vary across different contexts and crises? Do some types of crisis lead to more cross-border movement than others, and at what point do IDPs decide to flee beyond their own borders? More systematic data would allow us to analyse both historical and forward-looking trends, and to make comparisons between countries and regions. These in turn would be useful planning tools for governments and humanitarian and development agencies to better prepare for and respond to large flows of people such as those Europe has experienced over the last few years. To achieve this, data collection will have to be more joined-up. At the very minimum, datasets on IDPs, migrants, refugees and asylum-seekers need to be aligned and interoperable, and based on complementary definitions, standards and methods that are systematically applied. Those gathering data should strive for joint and regular