2020 Democratic Party presidential primaries

The 2020 Democratic Party presidential primaries and caucuses were a series of elections by the Democratic Party to select the about 3,979 pledged delegates to the Democratic National Convention. Those delegates picked the Democratic nominee for president of the United States in the 2020 United States presidential election.
The elections took place from February to August 2020 in all fifty U.S. states, the District of Columbia, five U.S. territories, and Democrats Abroad.
On June 5, 2020, Biden passed the threshold of 1,991 delegates, securing the nomination.
Background.
The 2020 field of Democratic presidential candidates peaked at more than two dozen candidates. According to "Politifact", this field is believed to be the largest field of presidential candidates for any American political party since 1972; it exceeds the field of 17 major candidates who sought the Republican presidential nomination in 2016. 
In May 2019, CBS News referred to the field of 2020 Democratic presidential candidates as "the largest and most diverse Democratic primary field in modern history", including at least six female presidential candidates.
Delegate votes.
The new superdelegate reforms also regulate how the 2020 Democratic National Convention shall handle the outcome of primaries and caucuses for three potential scenarios:
Primary and caucus calendar.
Note: Due to COVID-19, most primaries after March 10 were rescheduled. 
Convention.
The convention was scheduled to be held from July 13–16, 2020, at the Fiserv Forum in Milwaukee, Wisconsin. Because of the COVID-19 pandemic, it was held from August 17–20. Most speakers did not go to the central location. Instead, they joined the convention from other places, using the internet.