U2 regained critical success with their tenth studio album.
U2 . The group 's fifth album , The Joshua Tree ( 1987 ) , made them international superstars and was their greatest critical and commercial success . This experimentation continued through their ninth album , Pop ( 1997 ) , and the PopMart Tour , which were mixed successes . The group 's thirteenth album , Songs of Innocence ( 2014 ) , was released at no cost through the iTunes Store , but received criticism for its automatic placement in users ' music libraries .