[2] Nineteen countries participated in the contest, with Albania, Armenia, Ireland, Italy, North Macedonia and Portugal all returning after their absence from the previous edition.

The selected venue for the contest was the 6,000-seat La Seine Musicale, which serves as concert hall and performing arts center.

[4][5] Unlike Eurovision's adult version, the winning country originally did not receive the automatic rights to host the next contest.

On 15 October 2017, the EBU announced a return to the original system in 2018, to help provide broadcasters with a greater amount of time to prepare, and to ensure the continuation of the contest into the future.

[3] The French Head of Delegation Alexandra Redde-Amiel had previously stated that France Télévisions was keen to host the contest.

[9] Le Parisien reported in September 2021 that France Télévisions had looked into the possibility of organising the contest in Cannes or Nice before settling on the metropolitan area of Paris as a precaution against the COVID-19 pandemic, and that Paris La Défense Arena was considered a potential venue in a 8,000-seat configuration before La Seine Musicale was named the chosen venue.

For the first time since the contest's inception, Belarus did not participate, as the country's broadcaster BTRC is in the midst of a three-year suspension from the EBU.

Prior to the event, a digital compilation album featuring all the songs from the 2021 contest was put together by the European Broadcasting Union and released by Universal Music Group on 3 December 2021.

[27][28] The slogan was chosen as a reference to the previous year's winning song "J'imagine", as well as a way to encourage children to be creative and pursue their dreams.

[30] Contestants were featured in "postcard" video introductions, set in a different location in Paris, or surrounding areas in France.

The opening of the show featured the traditional flag parade, accompanied by French DJ duo Ofenbach performing a medley of their discography.

[50] For a country to be eligible for potential participation in the Junior Eurovision Song Contest, it needs to be an active member of the EBU.

[92] According to the EBU, 33 million people watched the Junior Eurovision Song Contest 2021, with a viewing share of 15.6%.