A humanitarian crisis (or sometimes humanitarian disaster) is defined as a singular event or a series of events that are threatening in terms of health, safety or well-being of a community or large group of people. It may be an internal or external conflict and usually occurs throughout a large land area. Local, national and international responses are necessary in such events.

Each humanitarian crisis is caused by different factors and as a result, each different humanitarian crisis requires a unique response targeted towards the specific sectors affected. This can result in either short-term or long-term damage. Humanitarian crises can either be natural disasters, human-made disasters or complex emergencies. In such cases, complex emergencies occur as a result of several factors or events that prevent a large group of people from accessing their fundamental needs, such as food, clean water or safe shelter.

Common causes of humanitarian crises are wars, epidemics, famine, natural disasters, energy crises and other major emergencies. If a crisis causes large movements of people it could also become a refugee crisis. For these reasons, humanitarian crises are often interconnected and complex and several national and international agencies play roles in the repercussions of the incidences.

There is no simple categorization of humanitarian crises. Different communities and agencies tend to have definitions related to the concrete situations they face. A local fire service will tend to focus on issues such as flooding and weather induced crises. Medical and health related organizations are naturally focused on sudden crises to the health of a community.

Humanitarian crisis may arise from both natural and human-made conflicts and disasters. Humanitarian crisis from natural disasters include tsunami, earthquake, hurricane, floods, droughts, and wildfires that may result in disruption through damage to property, physical injury and death, psychological distress, displacement of individuals and families, and prolonged disruption in normal daily activities. On the other hand, crisis from manmade disasters such as wars, social unrest, protests, conflicts, and terrorist attacks have a broad range of impacts on the physical, mental, and social well-being of the individuals affected.

An ongoing or lingering pandemic may amount to a humanitarian crisis, especially where there are increasing levels of virulence, or rates of infection as in the case of AIDS, bird flu or tuberculosis. Major health-related problems such as cancer, global warming typically require an accentuated or punctuated mass-event to justify a label of "crisis" or "disaster".

The International Federation of Red Cross and Red Crescent Societies (IFRC) lists categories which include different types of natural disasters, technological disasters (i.e. hazardous material spills, Chernobyl-type nuclear accidents, chemical explosions) and long-term human-made disasters related to "civil strife, civil war and international war". Internationally, the humanitarian response sector has tended to distinguish between natural disasters and complex emergencies which are related to armed conflict and wars.

Socially, women and children (mostly girls) receive a significantly decreased amount of attention in response to humanitarian crises. Women and children make up 3 quarters of refugees or displaced persons at risk post-crisis. A quarter of this population is of reproduction age and a fifth of this population is likely to be pregnant. In times of emergency and such crises, deaths associated with pregnancy, reproductive health, sexual violence and sexual exploitation increase drastically especially amongst females. During such emergencies, women lose access to family planning services, prenatal care, postpartum care and other health services. The heightened risk of female health and safety makes them vulnerable to disease, violence and death.