Who wrote the Quran?

How the revelation began

Muhammad ﷺ used to spend time alone in worship in a cave called Hira, near Mecca. There, the angel Gabriel came to him and told him to read. He replied that he did not know how to read, and after this was repeated, the first verses of Surah al-Alaq were revealed. He returned home shaking, and his wife Khadija comforted him (Sahih al-Bukhari 3). Over the following years, verses kept coming, often in response to real events in the community.

Why Muslims say it isn't the Prophet ﷺ's own words

• The Quran says so: it describes the Prophet ﷺ as speaking by revelation, not from himself.
• He couldn't read or write: the Quran points out that he had not read earlier scriptures or written anything before it (Quran 29:48).
• Its style is distinct: the Prophet ﷺ's own sayings (hadith) were recorded separately and sound different from the Quran. Muslims have always kept the two apart.
• It speaks to him: the Quran often addresses and sometimes corrects the Prophet ﷺ, which is unusual for a book someone writes about himself.

Who wrote it down?

Several Companions acted as scribes, the best known being Zayd ibn Thabit. After the Prophet ﷺ died, Zayd was asked to gather the whole Quran into one copy, collecting it from written pieces and from people's memories (Sahih al-Bukhari 4986). So "who wrote it down" has a clear historical answer, while "who authored it" is, for Muslims, Allah.

For more on how the text was kept, see Was the Quran changed over time?

What if I'm not sure yet?

Many non-Muslim historians see the Quran as coming from Muhammad himself in 7th-century Arabia. If you're exploring Islam, that's a fair question to wrestle with. The Quran invites this kind of thinking, asking people to reflect on it and challenging them to find contradictions (Quran 4:82). The best way to decide is to read it yourself, slowly, with a good translation. See Where should I start reading the Quran as a new Muslim?