The principles of humanity, impartiality, neutrality and independence are intended to enable, characterise and guide the delivery of humanitarian assistance. However, as conflicts grow more complex, interpretations of humanitarian principles are being questioned, particularly in areas under the control or influence of proscribed non-state armed groups (NSAGs). Delivery of aid in these areas may clash or be perceived to clash with principles of public accountability and transparency – principles which are paramount for many donor States. In several recent conflicts – particularly in protracted conflicts such as those in Syria, Afghanistan, Iraq and Somalia – the most vulnerable people are located in areas which are (or have been) controlled or heavily influenced by NSAGs such as the Islamic State, Al Qaeda and Al Shabaab and their affiliates. NSAGs such as these have been designated as terrorist groups by donor governments – and in some cases also by the UN. To reach the populations at risk, however, humanitarian actors need to engage with NSAGs, often through remote operations or through overcoming access restrictions. Engagement therefore entails an increased risk of aid diversion in a context where there are limited guidelines for acceptable degrees of risk. Recent compliance developments designed to ensure that aid supports the public good include tightening of anti-terrorism restrictions and reinforcing financial controls. In practice, these have reduced the ability of non-governmental organisations (NGOs) to reach the most vulnerable, in large part due to increased risk aversion and lack of clarity around the precise nature of the rules and regulations. Civilians in areas heavily influenced or controlled by NSAGs are frequently worse off than civilians in other areas due to the general lack of goods and services and the specific protection risks affecting vulnerable populations, including targeting of religious or ethnic minorities. Markets are disrupted because of obstructions in the transport network, such as fees being demanded at checkpoints. Supply chain difficulties are often exacerbated by the fact that NSAGs do not prioritise civilians in the distribution of goods. Services are halted due to reductions in government personnel and uncertainty surrounding political power dynamics and control. Overall, interruptions in markets and services have a disproportionate effect on the most vulnerable as the poor are less likely to be able to afford price increases. In some cases, NSAGs may take measures that reduce the well-being of the most vulnerable, for example by levying informal taxes on civilians or by excluding particular groups (often religious and ethnic minorities) from accessing goods and services. Provision of impartial needs- based assistance requires humanitarians to take active measures to reach populations in areas controlled by NSAGs.