League D is the bottom-tier of the UEFA Nations League pyramid.
Group 1 features four teams while Group 2 contains three.
The team finishing first in each group will be promoted to League C.
Group 1: Liechtenstein, Moldova, Latvia & Andorra
League D features Europe's minnow nations, but this competitions presents all teams with a realistic chance of claiming historic victories.
After suffering relegation as recently as March, Moldova are seeking an instant return to the third-tier.
Two years ago, they failed to win any of their six League C matches, so faced Kazakhstan in a two-legged relegation play-out.
The tie ended 2-2 on aggregate and, in the subsequent penalty shootout in Nur-Sultan, Ioan-Călin Revenco missed the decisive kick as his team went down.
Now though, playing in the bottom-division, Serghei Cleșcenco's side are strong favourites to top this section.
The other three teams in Group 1 are all preparing for a third successive campaign down in League D.
Andorra are still looking for their first-ever win in the Nations League, but have managed to draw six of 12 matches to date.
Koldo Álvarez's side did defeat San Marino home and away during World Cup qualifying last year, so are hopeful of more wins here.
Latvia are the only team in League D who've previously qualified for a major tournament, appearing at Euro 2004.
However, since ousting Turkey in a two-legged play-off 19 years ago, they've won just 24 of 109 competitive internationals.
Dainis Kazakevičs' side hammered Andorra 5-0 in this competition two years ago, but that remains their sole Nations League triumph to date.
Liechtenstein complete the quartet; they're currently winless in 18 matches, losing 15 of of them, conceding 34 goals in ten World Cup qualifiers.
The Blues-Reds beat Gibraltar in 2018 and San Marino two years ago, so will be optimistic that this tournament can end their wait for a win.
Prediction: 1st- Moldova. 2nd- Latvia. 3rd- Liechtenstein. 4th- Andorra.
Group 2: Malta, Estonia and San Marino
Estonia are the big boys of Group 2 and are overwhelming favourites to make an immediate return to League C.
The Blueshirts are competing at this level for the first time having been beaten 2-0 by Cyprus in March's relegation play-outs.
This means Estonia have only won one of 14 Nations League fixtures, a shock 1-0 victory in Athens against Greece four yeas ago.
Thomas Häberli's team are far from international heavyweights, but should still have far too much quality when competing at this level.
Malta will be their biggest challengers to top spot.
The Reds only lost once in this competition in 2020, but were pipped to promotion by Faroe Islands.
Then, last year, Devis Mangia's side impressed in World Cup qualifying, hammering Cyprus 3-0 whilst also drawing away in Slovakia and Cyprus.
Given this, the matches in Ta' Qali and Tallinn on 9 June and 23 September and likely to be crucial in the battle for promotion.
San Marino round-out the trio, still seeking their first-ever competitive win.
La Serenissima held both Liechtenstein and Gibraltar to goalless draws in this competition two years ago, but a first win still alludes them.
Their record in competitive fixtures stands at this: Played 162. Drawn 5. Lost 157. Won Zero. Goals conceded 715.
Fabrizio Costantini's side will be particularly targeting their two games in Serravalle as they seek to make history.
Prediction: 1st- Estonia. 2nd- Malta. 3rd- San Marino.