Pink Floyd were an English rock band who in the 1960s earned recognition for their psychedelic and space rock music, and in the 1970s, as they evolved, for their progressive rock music. Pink Floyd's work is marked by philosophical lyrics, sonic experimentation, innovative album cover art, and elaborate live shows. One of rock music's most critically acclaimed and commercially successful acts, the group has sold over 200 million albums worldwide including 74.5 million certified units in the United States. Pink Floyd influenced progressive rock artists of the 1970s including Genesis and Yes, as well as contemporary artists such as Nine Inch Nails and Dream Theater.