How many teams go through from each group in Euro 2016?

Question

I just noticed that there are 6 groups in the current European Championships, which means that - if the top two from each group were to go through - there would only be 12 teams into the last 16, which is 4 short.

However, if the top 3 from each group go through, we get 18 teams going to the round of 16, which is 2 too many.

There would have to be just 4 groups where 3 teams go through and 2 groups where the top 2 go through to make 16 teams in the round of 16.

How is it working?

Are there 4 groups where 3 teams go through? If so, how do they decide which groups?

Answer 1

16 teams will progress to the knockout stages of Euro 2016 from the group stages. The top two sides from each group will qualify, followed by 4 of the 6 third-placed team in the group.

The Wikipedia article for Euro 2016 explicitly explains the qualification process for the knockout stages. I have added an excerpt here for your benefit, emphasis mine.

To accommodate the expansion from a 16 team finals tournament to 24 teams, the format will be changed from that used in 2012 with the addition of two extra groups in the group stage, and an extra round in the knockout stages. The six groups (A to F) would still contain four teams each, with the top two from each group still going through to the knockout stage. In the new format however, the four best third-ranked sides would also progress, leaving 16 teams going into the new round of 16 knockout stage, ahead of the usual quarter-finals, semi-finals and final, and only 8 teams going out at the group stage. The format is exactly the one which was applied to the 1986, 1990 and 1994 FIFA World Cups, with the exception of the absence of a third-place play-off.

There is also a handy table in the Wikipedia article which shows how the third-placed teams are ranked currently.

Answer 2

Euro 2016 is open to 24 teams while since 2012 was to 16 when the firsts and the seconds teams qualify for the knockout rounds.

This expansion required a modification to the first round of the qualification system and those are the criteria for the qualification:

1. Points
2. Goal difference
3. Goals scored
4. Fair play (3 pts for a red card, 1 pt for a yellow, lowest score wins)
5. UEFA team coefficient

Here you can find a detailed article

The four best third teams will play knockout against the winner of the groups A-B-C-D