Willemsen may refer to:
The Sidecar Motocross World Championship is an annual event, first held in 1980. It is organized by the Fédération Internationale de Motocyclisme (FIM). Before 1980, a European competition was held from 1971 onwards.
Daniël Johan Nico Willemsen is a Dutch sidecarcross rider and ten times World Champion.
Kristers Serģis is a retired Latvian sidecarcross rider and five times World Champion.
Kaspars Stupelis is a Latvian sidecarcross passenger and quadruple World Champion.
The 2008 FIM Sidecarcross world championship, the 29th edition of the competition, started on 20 April and finished after twelve race weekends on 14 September 2008. Daniël Willemsen and Reto Grütter were the defending champions, having won the title in 2007, and repeated this achievement in 2008.
Reto Elias Grütter is a Swiss sidecarcross passenger and the 2007 and 2008 Sidecarcross World Champion.
Sven Verbrugge is a retired Belgian sidecarcross passenger and triple Sidecarcross World Champion, winning the title in 2005, 2006 and 2011.
Marcel Willemsen is a Dutch sidecarcross passenger and 1999 World Champion.
Artis Rasmanis is a retired Latvian sidecarcross passenger and five times World Champion.
The Vruwink MotorCycles company, short VMC, is a Dutch Sidecarcross frame manufacturer, having won eleven riders and six manufacturers world championships in this sport.
The 2004 FIM Sidecarcross World Championship, the 25th edition of the competition, started on 21 March 2004 and finished after fourteen race weekends on 5 September 2004 with Daniël Willemsen and Kaspars Stupelis taking out the title once more. For Willemsen, it was his third world championship while it was the second for Stupelis.
Joris Hendrickx is a Belgian sidecarcross rider and the 2009 World Champion, together with his passenger, the Latvian Kaspars Liepiņš.
Kaspars Liepiņš is a Latvian sidecarcross rider and the 2009 World Champion, won as the passenger of the Belgian Joris Hendrickx.
The 2012 FIM Sidecarcross World Championship, the 33rd edition of the competition, started on 1 April and finished after eleven race weekends on 16 September 2012.
Gertie Eggink is a Dutch sidecarcross rider and the 2010 Sidecarcross World Champion, riding as passenger with Daniël Willemsen.
Kenny van Gaalen is a Dutch sidecarcross rider and the 2012 Sidecarcross World Champion, riding as passenger with Daniël Willemsen.
Ben Adriaenssen is a Belgian sidecarcross rider and the 2013 and 2014 World Champion, together with his Dutch passenger, Ben van den Bogaart.
The 2013 FIM Sidecarcross World Championship, the 34th edition of the competition, started on 1 April and finished after fourteen race weekends on 22 September 2013.
Fritz Fuß is a retired Swiss sidecarcross passenger and four times Sidecarcross World Champion, having won the competition from 1984 to 1987 as the passenger of Hansi Bächtold. The duo became the first-ever combination to win the competition four times in a row, a feat later repeated by the Swiss team of Andreas Fuhrer and Adrian Käser and surpassed by Dutch rider Daniël Willemsen with six consecutive titles.
The 2000 FIM Sidecarcross World Championship, the 21st edition of the competition, started on 19 March and finished after thirteen Grand Prix on 24 September 2000.