OCHA is the arm of the United Nations Secretariat responsible for bringing together humanitarian actors to ensure a coherent response to emergencies, with the aim of assisting people when they most need relief or protection. A key pillar of the OCHA mandate is to “coordinate effective and principled humanitarian action in partnership with national and international actors”.
Humanitarian coordination seeks to improve the effectiveness of humanitarian response by ensuring greater predictability, accountability and partnership. OCHA is leading the international community's efforts to develop a better architecture for the humanitarian system, including strong in-country humanitarian leaders (Humanitarian Coordinators); representative and inclusive Humanitarian Country Teams; an effective and well-coordinated framework within which all humanitarian organizations can contribute systematically; and predictable funding tools.
OCHA plays a key role in operational coordination in crisis situations, including assessing situations and needs, agreeing common priorities, and developing common strategies to address issues such as negotiating access, mobilizing funding and other resources, clarifying consistent public messaging, and monitoring progress. OCHA also administers the cluster coordination system for the Humanitarian Coordinator, including meetings, data and information management, and reporting.  
Ensuring that the right structures, partnerships and leaders are supported means that OCHA and its humanitarian partners can better prepare for and more effectively coordinate humanitarian situations.
OCHA serves as the secretariat for critical inter-agency coordination mechanisms such as the Inter-Agency Standing Committee; rapid-response tools, such as the United Nations Disaster Assessment and Coordination system, and the International Search and Rescue Advisory Group. OCHA also promotes efficient interaction between civilian and military actors in humanitarian operations, bridges gaps in environmental emergency management, and maps global emergency relief stockpiles on behalf of the whole humanitarian community.
Key to effective response is the state of preparedness in advance of a crisis: OCHA promotes the value of preparedness in lessening the impact of disasters on vulnerable communities, especially in disaster-prone countries. We work with national governments, regional bodies and other agencies on implementing and testing measures that really help save lives in an emergency, as well as providing tools such as contingency planning, hazard mapping and early warning reports.  
Working through a system of regional and country offices, OCHA deploys staff at short notice to emergencies. It also supports several "surge capacity" mechanisms and networks that enable the broader humanitarian community to respond rapidly to disasters and conflicts.