Korea's 50 years of economic development
 Artikel Jurnal
Drucker, Peter Ferdinand, 1909-2005
America's next twenty years
Harper & Brothers, 1957
 Buku Teks SO
Davidson, Jamie S.
Indonesia: twenty years of democracy
Cambridge University Press, 2018
 Buku Teks SO
Celebrating twenty years with Deloitte in Indonesia
Deloitte Touche Tohmatso limited
Deloitte Touche Tohmatso limited, 2010
 Buku Referensi
Gielzynski, Woijciech
Poland
Arkady, 1994
 Buku Teks SO