Scientists' increasing recognition of an interconnected Earth system and the need to pursue global sustainability has led to repeated calls, over the past three decades, for interdisciplinary and more recently transdisciplinary research into global environmental change (GEC). Interdisciplinary and transdisciplinary research are similar to the extent that they entail varied degrees of science integration. Transdisciplinary research involves transcending disciplines and engaging with non-academics throughout the research process, while broad interdisciplinary research happens when researchers across the natural and social sciences collaborate to tackle societal problems and produce new and insightful knowledge and possible solutions. This would have been impossible had they remained within single disciplinary confines. Such science integration raises awareness of the required focus on the nexus between human and environmental systems in order to achieve sustainability. Yet progress in science integration has only been incremental and remains limited. This paper elucidates an evolving conceptualisation of integration, identifies barriers and describes opportunities to dismantle persistent impediments to integration. Contemporary understanding of integration entails three dimensions: (i) scientific integration, involving integration across academic (natural, social and human science) disciplines, (ii) international integration, involving integration from local to global and across nations and cultures, and (iii) sectoral integration, involving integration across science and society. Persistent barriers must, however, be overcome and experiences documented and shared in order to enable transdisciplinary GEC research for sustainability to cross disciplinary, sectoral and international boundaries.