"The Bonnie Blue Flag", also known as "We Are a Band of Brothers", is an 1861 marching song associated with the Confederate States of America. The words were written by the entertainer Harry McCarthy, with the melody taken from the song "The Irish Jaunting Car". The song's title refers to the unofficial first flag of the Confederacy, the Bonnie Blue Flag. The left flag on the sheet-music is the Bonnie Blue Flag.
The song was premiered by lyricist Harry McCarthy during a concert in Jackson, Mississippi, in the spring of 1861 and performed again in September of that same year at the New Orleans Academy of Music for the First Texas Volunteer Infantry regiment mustering in celebration.
The New Orleans music publishing house of A.E. Blackmar issued six editions of "The Bonnie Blue Flag" between 1861 and 1864 along with three additional arrangements.
The "band of brothers" mentioned in the first line of the song recalls the well known St. Crispin's Day Speech in William Shakespeare's play Henry V (Act IV, scene ii).