A collective trauma is a psychological effect on an entire society. Traumatic events that emotionally touch nearly every member of said society will often induce a collective trauma. As a result of such trauma, often media, politicians and, in some extreme instances, the general public, will start looking for scapegoats. Collective traumas often give rise to conspiracy theories.

In hindsight, collective traumas will often be watersheds of history and signify or initiate times of change in the society affected.

Well known collective traumas include: The John F. Kennedy assassination in the United States, the Estonia disaster in Sweden and various others.

The destruction of the World Trade Center in the September 11, 2001 Terrorist Attack was expected to induce a severe collective trauma in US society. While much of the country, especially around New York were shocked, studies have found that incidents of suicide and depression did not noticeably increase.