Early in 2018, the United Nations Development Program’s Human Development Report Office (HDRO) and the Oxford Poverty and Human Development Initiative (OPHI) agreed to adjust and unify their methodologies on poverty measurement and consider indicator improvements, in order to better monitor the Sustainable Development Goals (SDGs). This paper sets out the specifications of a joint global Multidimensional Poverty Index first published in 2018, which is an internationally comparable measure of acute poverty that captures the multiple deprivations poor people experience with respect to health, education and living standards. It builds on the original MPI launched in 2010, and an innovative MPI launched in 2014. The best features of both of these are subsumed in the joint global MPI 2018, which also reflects new data possibilities to better align the global MPI to the Sustainable Development Goals. Because the objective of revising the MPI to create a more credible and legitimate measure of multidimensional poverty that enables comparisons across countries using existing data was challenging to realize, the paper first sets out five key principles for a global poverty measure related to data coverage, communicability, comparability, disaggregation, and robustness. Drawing on expert interventions, a global consultation, empirical trials, and these principles, the paper then explains conceptually the motivation and nature of adjustments that were made to five of the ten included indicators. It also recognizes desirable changes that could not be made due to data constraints – for example including data on the environment, work, and security, or on intrahousehold inequalities. And it identifies key issues for future research related to household composition and the use of land and livestock variables.