The best-selling works of the 20th century are estimated to be `` Quotations from Chairman Mao '' ( 1966 , 900 million copies ) , `` Harry Potter and the Philosopher 's Stone '' ( 1997 , 120 million copies ) , `` And Then There Were None '' ( 1939 , 115 million copies ) and `` The Lord of the Rings '' ( 1954/55 , 100 million copies ) .
The best-selling works of the 20th century are thought to be `` Quotations from Chairman Mao '' ( 1966 , 900 million copies ) , `` Harry Potter and the Philosopher 's Stone '' ( 1997 , 120 million copies ) , `` And Then There Were None '' ( 1939 , 115 million copies ) and `` The Lord of the Rings '' ( 1954/55 , 100 million copies ) .