"Ring a Ring o' Roses", also known as "Ring a Ring o' Rosie" or "Ring Around the Rosie", is a nursery rhyme, folk song, and playground game. Descriptions first appeared in the mid-19th century, though it is reported to date from decades earlier. Similar rhymes are known across Europe, with varying lyrics. It has a Roud Folk Song Index number of 7925.

The origin of the song is unknown. Pagan myth or folklore were proposed as origins at the end of the 19th century. In the mid-20th-century, it was suggested that the song reflects the Great Plague or earlier outbreaks of bubonic plague in England, with the plague's rash, protective posies of herbs, symptoms of sneezing, and finally falling down dead. However, the symptoms do not align closely with the song; the explanation emerged centuries after the plague; and European and 19th-century versions of the song do not match the interpretation either.

In popular culture, the plague interpretation has taken hold, with a variant version on nuclear war.

The origins and earliest wording of the rhyme remain unknown. In many versions of the game, a group of children forms a ring, dances in a circle around one person, and then stoops or curtsies on the final line. The slowest child to perform this action may face a penalty or become the "rosie" (literally: rose tree, from the French rosier), taking their place in the center of the ring.

Common British versions include:

Ring-a-ring o' roses,
A pocket full of posies.
A-tishoo! A-tishoo!
We all fall down!

Common American versions include:

Ring around the rosie,
A pocket full of posies.
Ashes! Ashes!
We all fall down!