The 12 teams will be split into four groups of three, with the top teams promoted and bottom teams relegated at the end of the six games.
UEFA have also confirmed that Nations League games will stand as "competitive" replacements for worldwide friendlies, but not as a replacement for the Euro 2020 qualifying campaign, which will now begin in March 2019 and end in November 2019.
Germany, Portugal, Belgium and Spain are the top seeds and can not play each other, with France, England, Switzerland and Italy in pot 2.
The draw for the groups within each league will take place on 24th January 2018.
March 2020 will see the play-offs for Euro 2020, with the final tournament to be held in 13 cities across Europe, including Dublin, in June-July.
Country coefficients and the recently concluded World Cup qualifying helped determine which nations would be drawn into the four different leagues - A, B, C, D.
Euro 2020 qualifying will then take place between March and November 2019, with the Uefa Nations League Finals for the top four teams in June 2019.
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Today it was announced which teams will feature in the four leagues.
The tournament, which features all 55 Uefa members, will largely replace worldwide friendlies during the qualification period for the European Championship in 2020.
League C will be made up of three groups of four teams and one group of three.
League B: Austria, Wales, Russia, Slovakia, Sweden, Ukraine, Republic of Ireland, Bosnia and Herzegovina, Northern Ireland, Denmark, Czech Republic, Turkey.
League C contains Hungary, Romania, Scotland, Slovenia, Greece, Serbia, Albania, Norway, Montenegro, Israel, Bulgaria, Finland, Cyprus, Estonia and Lithuania.
There are four tiers and nations have been placed with teams of similar ability.
For example, with League D guaranteed a representative, Azerbaijan, Macedonia, Belarus and Latvia are the favourites to battle it out over a series of one-off contests to join, but not necessarily be competitive in, the finals jamboree.
The qualification for Euro 2020 will now now run from March to November 2019, with Dublin hosting the Group draw on 2 December 2018.