"Matty Groves", also known as "Little Musgrave and Lady Barnard" or "Little Musgrave", is a ballad probably originating in Northern England that describes an adulterous tryst between a young man and a noblewoman that is ended when the woman's husband discovers and kills them. It is listed as Child ballad number 81 and number 52 in the Roud Folk Song Index. This song exists in many textual variants and has several variant names. The song dates to at least 1613, and under the title Little Musgrave and Lady Barnard is one of the Child ballads collected by 19th-century American scholar Francis James Child.

Little Musgrave (or Matty Groves, Little Matthew Grew and other variations) goes to church on a holy day either "the holy word to hear" or "to see fair ladies there". He sees Lord Barnard's wife, the fairest lady there, and realises that she is attracted to him. She invites him to spend the night with her, and he agrees when she tells him her husband is away from home. Her page overhears the conversation and goes to find Lord Barnard (Arlen, Daniel, Arnold, Donald, Darnell, Darlington) and tells him that Musgrave is in bed with his wife. Lord Barnard promises the page a large reward if he is telling the truth and to hang him if he is lying. Lord Barnard and his men ride to his home, where he surprises the lovers in bed. Lord Barnard tells Musgrave to dress because he doesn't want to be accused of killing a naked man. Musgrave says he dare not because he has no weapon, and Lord Barnard gives him the better of two swords. In the subsequent duel Little Musgrave wounds Lord Barnard, who then kills him. (However, in one version "Magrove" instead runs away, naked but alive.)

Lord Barnard then asks his wife whether she still prefers Little Musgrave to him and when she says she would prefer a kiss from the dead man's lips to her husband and all his kin, he kills her. He then says he regrets what he has done and orders the lovers to be buried in a single grave, with the lady at the top because "she came of the better kin". In some versions Barnard is hanged, or kills himself, or finds his own infant son dead in his wife's body. Many versions omit one or more parts of the story.

It has been speculated that the original names of the characters, Little Musgrave and Lady Barnard, come from place names in the north of England (specifically Little Musgrave in Westmorland and Barnard Castle in County Durham). The place name "Bucklesfordbury", found in both English and American versions of the song, is of uncertain origin.

Some versions of the ballad include elements of an alba, a poetic form in which lovers part after spending a night together.

There are few broadside versions. There are three different printings in the Bodleian Library's Broadside Ballads Online, all dating from the second half of the seventeenth century. One, The lamentable Ditty of the little Mousgrove, and the Lady Barnet from the collection of Anthony Wood, has a handwritten note by Wood on the reverse stating that "the protagonists were alive in 1543".

Below are the first four verses as written in a version published in 1658.

As it fell one holy-day, hay downe,
As many be in the yeare,
When young men and maids
Together did goe,
Their Mattins and Masse to heare,

Little Musgrave came to the church dore,
The Preist was at private Masse
But he had more minde of the faire women;
Then he had of our lady grace

The one of them was clad in green
Another was clad in pale,
And then came in my lord Bernards wife
The fairest amonst them all;

She cast an eye on little Musgrave
As bright as the summer sun,
And then bethought this little Musgrave
This lady's heart have I woonn.