Garrison, D. R. (D. Randy), 1945-
E-learning in the 21st century : a community of inquiry framework for research and practice
Routledge, 2017
 Buku Teks
European integration in the 21st Century: unity in diversity?
Sage Publications, 2012
 eBooks
Tan, Oon-Seng
Problem-based learning innovation: using problems to power learning in the 21st century / oon-Seng Tan
Thomson Learning, 2003
 Buku Teks
Town planning into the 21st century
edited by Andrew Blowers, Bob Evans
Routledge, 1997
 Buku Teks SO
The 21st century world atlas
Trident Press, [Date of publication not identified]
 Buku Referensi