In a small number of crisis-affected countries, humanitarian organizations work amid active conflict and under direct threat of violence. This insecurity, reflected in rising aid worker casualty rates, significantly constrains humanitarian operations and hinders the ability of people in emergencies to access vital aid. Extensive fieldbased research in Afghanistan, southern Somalia, South Sudan and Syria measured humanitarian coverage (aid presence relative to the level of need) in each context to determine how this coverage is affected by insecurity. Results show that humanitarian operations are highly determined by security conditions, more than any other factor. As a result, coverage is uneven relative to need and appears politically skewed in favor of areas under control of Western-supported conflict parties. Additionally, humanitarian coverage in these war zones is even lower than it outwardly appears, as aid organizations tend to remain in the country (even after suffering attacks) but reduce and contract their field presence, adopting new, often suboptimal, means of programming.