The day is celebrated in an effort to raise awareness about Down syndrome and to advocate for the rights, inclusion, and well-being of people with Down syndrome.
The date was selected because Down syndrome is caused by the presence of a third copy of the 21st chromosome, and 21/3 (March 21st) represents this genetic condition.
This day was first observed on March 21, 2006.
It was officially recognized by the United Nations General Assembly in 2011.