Sūrat ar-Raḥmān (Arabic: سورة الرحمان‎, "The Most Merciful") is the 55th surah of the Qur'an with 78 ayats. It has the refrain: "Then which of your Lord's blessings would you both deny?"

One of the main aims of the sura is to chastise men and jinn for their lack of gratitude towards Allah, who has showered them with an abundance of blessings. Verses 1-30 describe some of the resources (fruits, palm trees, husked grain, fragrant plants, fresh and salt water, pearls, ships) that Allah has graciously provided for the men and jinn he created, in his infinite mercy, out of clay and smokeless fire (55:14), and set down under a sky illuminated by the twin risings of the sun and moon (55:17). In addition to these material blessings, verses 1-4 recount the fact that Allah taught man how to communicate and even gave him the Qur'an to guide him on the path to righteousness. The refrain, "Which, then, of your Lord’s blessings do you both deny?", chastises the bountifully-provided for men and jinn for failing to acknowledge their indebtedness to Allah for his tremendous mercy. The punishment that awaits these ungrateful creatures is briefly described in verses 35-45; for the remainder of the sura, the delights of the gardens of paradise (replete with shading branches, flowing springs, fruit, maidens, couches, cushions, and fine carpets) are lyrically described, punctuated throughout by the stinging refrain which draws attention to the discrepancy between Allah’s mercy in providing such luxuriant rewards and the ingratitude of men and jinn.

The idea that man’s gratitude towards Allah is not commensurate with Allah’s tremendous mercy is a central, recurring theme in the Qur'an, especially in the early Meccan suras, and Sura 55 is an important poetic treatment of this theme. The sura also exemplifies the Qur'an’s tendency to be self-referential and self-validating, as when in verse 2 it emphasizes the fact that Allah taught the Qur'an to man out of mercy.