Humanitarian supply chains are more expanded and global than ever before. Humanitarian organizations, alongside their development counterparts, work around the clock to satisfy the needs of beneficiaries, whether it is an armed conflict in the Middle East, a refugee crisis in Europe, or an ongoing drought in Africa. Meeting the ever-growing humanitarian needs entails intense logistics operations from procurement, to transportation, warehousing, last-mile distribution, and reverse logistics. These operations contribute to considerable environmental impact. However, environmental sustainability has been overlooked in humanitarian supply chain research hitherto. The objective of this thesis is integrating humanitarian supply chain management with green supply chain management, two streams within the supply chain management literature which have been growing in isolation from one another.The thesis builds upon the contingency theory and proposes a theoretical underpinning to distinguish the peculiarities of humanitarian environment and investigate how such peculiarities impact on the adoption, customization, and development of green practices. An action research methodology was used in collaboration with an international humanitarian organization and two and a half cycles of collaboration were conducted to integrate environmental sustainability into their supply chains.The research reveals four key findings. First, it proposes a greening framework that frames the extant green practices in a suitable form for humanitarian organizations. Second, it unearths the barriers and enablers of greening humanitarian supply chains vis-à-vis intra-organizational management, organizational functions such as procurement, funding environment, as well as other stakeholders such as suppliers, other humanitarian organizations, and country offices. Third, it explores the mechanisms through which humanitarian organizations can deal with or benefit from the identified barriers and enablers viz. i) improving the visibility of headquarters over delegations through increased presence of staff and employing information and communication technologies to track products during lastmile distribution, ii) developing instructions to minimize scavenging during reverse logistics and disposal, iii) promoting cooperation among different implementing partners at each country, and iv) raising flexible funding and donors' awareness about sustainability, inter alia. Fourth, a carbon footprinting conducted within the action research showed that humanitarian supply chain designs with hubs replenished periodically outperforms the design with perpetual replenishment through direct shipments from suppliers to country offices in terms of global warming potential.Moreover, the research offers strong practical contributions by implementing action steps for greening humanitarian supply chains and investigating the success or failure of each step. It also makes methodological contributions to action research by identifying the challenges and opportunities for conduc...