Yā Sīn (also Yaseen; Arabic: يس‎) is the 36th sūrah of the Quran. It has 83 verses (āyāt). It is regarded an earlier "Meccan surah". Some scholars maintain that verse 12 is from the Medinan period. While the surah begins in Juz 22, most of it is in Juz 23.

The surah begins with the eponymous (muqatta'at) Arabic letters: يس (yā sīn). The meaning of the letters Ya Sin, while being primarily unknown, is debated amongst Muslim religious academics. One of the interpretations is "O human being!" referring to Muhammad since the verses that follow are translated as "By the Qur´an, full of Wisdom, Thou art indeed one of the messengers". Tafsir al-Jalalayn, a Sunni beginners exegesis (tafsir), concludes, "God knows best what He means by these [letters]."

Yasin is also one of the names of Muhammad, as reported in a saying of Ali, "I heard the Messenger of God say, 'Verily God has named me by seven names in the Quran: Muhammad, Ahmad (61:6), Ṭā-Hā, (20:1), Yā Sīn (36:1), thou enwrapped (Al-Muzzammil; 73:1), thou who art covered (Al-Muddathir; 74:1), and servant of God (ʿAbd Allāh; 72:19).'"

The surah focuses on establishing the Qur'an as a divine source, and it warns of the fate of those who mock God's revelations and are stubborn. The surah tells of the punishments that plagued past generations of nonbelievers as a warning to present and future generations. Additionally, the surah reiterates God's sovereignty as exemplified by His creations through signs from nature.