Fridman, Leonid, editor
Sliding modes after the first decade of the 21st century : state of the art
Springer, 2011
 eBooks
Bocher, Erwan, editor
Geospatial free and open source software in the 21st century : proceedings of the first Open Source Geospatial Research Symposium, OGRS 2009
Springer, 2012
 eBooks
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
Ward, Ralph D.
21st century corporate board
John Wiley & Sons, 1997
 Buku Teks SO