Guillaume Costeley (c.1530-1606) was a French Renaissance composer and organist, active in the brilliant musical culture of sixteenth-century France. He served the French royal court and was associated with the world of the chanson and humanist poetry.

Costeley’s music includes chansons, sacred works and pieces connected with the movement known as musique mesurée, which sought to reflect the rhythms of classical verse in French song. His collection Musique, published in 1570, is an important source.

His style ranges from elegant lyricism to bold harmonic experiment. Some of his chansons are charmingly direct, while others show a striking taste for expressive chromatic colour.

Costeley stands among the important French song composers between the older Renaissance chanson and later Baroque declamation. His music has the poise of court art, but also the occasional raised eyebrow of a composer who enjoyed testing the walls.