"Rock-a-bye baby on the tree top" (sometimes "Hush-a-bye baby on the tree top") is a nursery rhyme and lullaby. It has a Roud Folk Song Index number of 2768.

The rhyme exists in several versions. One modern example, quoted by the National Literacy Trust, has these words:

Rock a bye baby on the tree top,
When the wind blows the cradle will rock,
When the bough breaks the cradle will fall,
And down will come baby, cradle and all.

The rhyme is believed to have first appeared in print in Mother Goose's Melody (London c. 1765), possibly published by John Newbery, and which was reprinted in Boston in 1785. No copies of the first edition are extant, but a 1791 edition substitutes "Hush-a-by baby" at the start of the first line. The rhyme is followed by a note: "This may serve as a warning to the proud and ambitious, who climb so high that they generally fall at last."

James Orchard Halliwell, in his The Nursery Rhymes of England (1842), notes that the third line read "When the wind ceases the cradle will fall" in the earlier Gammer Gurton's Garland (1784) and himself records "When the bough bends" in the second line and "Down will come baby, bough, cradle and all" as the fourth.

The scholars Iona and Peter Opie note that the age of the words is uncertain, and that "imaginations have been stretched to give the rhyme significance". They list a variety of claims that have been made, without endorsing any of them:

In Derbyshire, England, one local legend has it that the song relates to a local character in the late 18th century, Betty Kenny (Kate Kenyon), who lived in a huge yew tree in Shining Cliff Woods in the Derwent Valley, where a hollowed-out bough served as a cradle.

Another speculation was that the words "may simply have been suggested by the swaying and soothing motion of the topmost branches of the trees, although…another authority is that Rock-a-bye baby and Bye baby bunting come to us from the Indians, as they had a custom of cradling their pappooses among the swaying branches."