Town planning into the 21st century
edited by Andrew Blowers and Bob Evans
Routledge, 1997
 Buku Teks
Makridakis, Spyros G.
Forecasting, planning, and strategy for the 21st century
The Free Press, 1990
 Buku Teks
Gesker, Ronald D.
Media planning and buying in the 21st century
2020:Marketing Communications LLC, 2015
 Buku Teks
The 21st century world atlas
Trident Press, [Date of publication not identified]
 Buku Referensi
Ward, Ralph D.
21st century corporate board
John Wiley & Sons, 1997
 Buku Teks SO