XO-1 is a magnitude 11 G-type main-sequence star located approximately 530 light-years away[2] in the constellation Corona Borealis.

In 2006 the extrasolar planet XO-1b was discovered orbiting XO-1 by the transit method using the XO Telescope.

[9][10][11] The XO Project is an international team of professional and amateur astronomers which discovered the Jupiter-sized planet orbiting around XO-1.

The team, led by Peter R. McCullough of the Space Telescope Science Institute in Baltimore, includes four amateur astronomers from North America and Europe.

Further observations with the NICMOS instrument on board the Hubble Space Telescope detected the presence of water vapor, methane, and carbon dioxide in the atmosphere of XO-1b.