[1] Tim Reeves and Mark Wilkes entered the season as the reigning Driver and Passenger Sidecar World Champions respectively having won the championship in 2019.
[citation needed] Scott Lawrie is due to return to the championship in 2021 with former Bennie Streuer passenger, Ilse de Haas.
[5] The French round in Le Mans was part of the 2021 24 Heures Motos event with the FIM Endurance World Championship.
[6] The British (Donington Park) and Dutch rounds was part of the United Kingdom and Netherlands FIM Superbike World Championship events.
[5] On 9 February 2021 it was announced that the World Sidecar Championship would no longer be part of the 2021 Bol d'Or event due to a lack of sufficient track time and facilities as a result of the COVID-19 pandemic and associated problems.
[14] A number of the teams took part in five days of pre-season testing beginning on 22 March at the Circuit du Val de Vienne in France.
[16] On 27 March During a French Superbike Championship Sidecar race at Le Mans, Josef Sattler with stand in passenger Ilse de Haas lost the bike under braking and crashed.
[17] On 9 April 2021 at a private test organised by the Bonovo Action by MGM team at Oschersleben, Streuer/Clément crashed heavily as a result of suspected suspension failure.