Islamophobia is the irrational fear of, hostility towards, or hatred of the religion of Islam or Muslims in general. Islamophobia is characterised as a form of religious or cultural bigotry in which Muslims are stereotyped as a geopolitical threat or a source of terrorism. Muslims, with diverse ethnic and cultural backgrounds on a worldwide scale, are often inaccurately portrayed by Islamophobes as a single homogeneous racial group.

The causes of increased Islamophobia across the world since the end of the Cold War are many. These include the quasi-racialist stereotypes against Muslims that proliferated through the Western media since the 1990s, the "war on terror" campaign launched by the United States after the September 11 attacks, the rise of the Islamic State in the aftermath of the Iraq War, terrorist attacks carried out by Islamist militants in the United States and Europe, anti-Muslim rhetoric disseminated by white nationalist organizations through the internet, and the radicalisation of Christian nationalist and far-right groups with growing hostility towards Muslims in the United States and the European Union.

A study conducted in 2013 revealed that Muslim women, especially those wearing headscarves or face veils, are more vulnerable to suffer from Islamophobic attacks than Muslim men. Due to the racialised nature of Islamophobic discrimination and attacks suffered by numerous Muslims in their daily lives, several scholars have asserted that Islamophobia has explicit racist dimensions. On 15 March 2022, the United Nations General Assembly adopted a resolution by consensus which was introduced by Pakistan on behalf of the Organisation of Islamic Cooperation that proclaimed March 15 as 'International Day To Combat Islamophobia'.

The exact definition of the term "Islamophobia" has been a subject of debate amongst Western analysts. Detractors of the term have proposed alternative terms, such as "anti-Muslim", to denote prejudice or discrimination against Muslims. It has been alleged, often by right-wing commentators, that the term is sometimes used to avoid criticism of Islam, by removing the distinction between racism and criticism of religious doctrine or practice. However, academics, activists and experts who support the terminology have denounced such characterisations as attempts to deny the existence of Islamophobia.

There are a number of other possible terms which are also used in order to refer to negative feelings and attitudes towards Islam and Muslims, such as anti-Muslimism, intolerance against Muslims, anti-Muslim prejudice, anti-Muslim bigotry, hatred of Muslims, anti-Islamism, Muslimophobia, demonisation of Islam, or demonisation of Muslims. In German, Islamophobie (fear) and Islamfeindlichkeit (hostility) are used. The Scandinavian term Muslimhat literally means "hatred of Muslims".

When discrimination towards Muslims has placed an emphasis on their religious affiliation and adherence, it has been termed Muslimphobia, the alternative form of Muslimophobia, Islamophobism, antimuslimness and antimuslimism. Individuals who discriminate against Muslims in general have been termed Islamophobes, Islamophobists, anti-Muslimists, antimuslimists, islamophobiacs, anti-Muhammadan, Muslimphobes or its alternative spelling of Muslimophobes, while religiously intolerant individuals motivated by a specific anti-Muslim agenda or bigotry have been described as being anti-mosque, anti-Shiites (or Shiaphobes), anti-Sufism (or Sufi-phobia) and anti-Sunni (or Sunniphobes).

The word Islamophobia is a neologism formed from Islam and -phobia, a Greek suffix used in English to form "nouns with the sense 'fear of – – ', 'aversion to – – '."

According to the Oxford English Dictionary, the word means "Intense dislike or fear of Islam, esp. as a political force; hostility or prejudice towards Muslims". It is attested in English as early as 1923 to quote the French word islamophobie, found in a thesis published by Alain Quellien in 1910 to describe "a prejudice against Islam that is widespread among the peoples of Western and Christian civilization". The expression did not immediately turn into the vocabulary of the English-speaking world though, which preferred the expression "feelings inimical to Islam", until its re-appearance in an article by Georges Chahati Anawati in 1976. The term did not exist in the Muslim world, and was later translated in the 1990s as ruhāb al-islām (رُهاب الإسلام) in Arabic, literally "phobia of Islam".