Town planning into the 21st century
edited by Andrew Blowers and Bob Evans
Routledge, 1997
 Buku Teks
Gesker, Ronald D.
Media planning and buying in the 21st century
2020:Marketing Communications LLC, 2015
 Buku Teks
Makridakis, Spyros G.
Forecasting, planning, and strategy for the 21st century
The Free Press, 1990
 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