ESL One Cologne 2015 was the sixth Counter-Strike: Global Offensive Major Championship that was held from August 14–18, 2015 at the Lanxess Arena in Cologne.^[1] It was organized by Electronic Sports League. The Cologne event was the first ESL tournament that required competitors to take drug tests, which all came up negative.^[2][3][4] The tournament had a total prize pool of US$250,000. The online livestream was viewed by around 27 million viewers with a peak of 1.3 million concurrent viewers.^[5]

Eight teams were in the playoffs. Fnatic, Luminosity Gaming, Natus Vincere, Ninjas in Pyjamas, Team EnVyUs, Team SoloMid, and Virtus.pro were returning Legends. Team Kinguin was the only new Legend in the tournament, replacing mousesports, which failed to make the top eight. Fnatic, which defeated Luminosity Gaming and Virtus.pro, was the winner of the event after defeating Team EnVyUs, which defeated Natus Vincere and Team SoloMid, 2–0.^[6] Fnatic was the first team to have consecutive major titles and would be the only team to do so until SK Gaming (which was Luminosity Gaming at this tournament) when the Brazilian team won MLG Columbus 2016 and ESL One Cologne 2016.

The top eight teams from ESL One Katowice 2015 ("Legends") received direct invitations to Katowice. In addition, eight other teams (the "Challengers") emerged from offline qualifiers: four from the European qualifier, two from the Asian qualifier, and two from the North American qualifier.

Teams were split up into four groups, and all group matches were best-of-ones. In the first group stage, the highest seed played the lowest seed in each group and the second and third seeds played each other. The winner of those two matches then played each other to determine which team moved on to the playoff stage; the loser of this match received a "high seed" in the second group stage. The two losers from the initial matches were given "low seeds" in the second group stage, while the high seed received a bye. In the second group stage, the groups were shuffled so that teams faced new opponents.^[7] However, each group still contained one high seed and two low seeds. The two low seeds in each group played each other, and the winner of that match played the high seed in the group. The winner of that match qualified for the playoff stage.

The playoffs bracket consisted of eight teams, two from each group. All of these matches were best-of-three, single elimination. Teams advanced in the bracket until a winner was decided.

Four teams from the European Qualifier, two teams from the Asian Qualifier, and two teams from the North American Qualifier moved on to the major.

Sixteen European teams were placed in two separate brackets. Two teams from each bracket moved on to the major. In the Asian and North American Qualifiers, eight teams were placed in two groups and were played out like in previous majors' group stages. The top two moved on to a four team bracket. The winners of the matches move on to the major.^[8]

North American Qualifier

NA Qualifier Bracket; Burbank, California

	Semifinals					Qualified
	Cloud9		2
	eLevate		0
						Cloud9
						Counter Logic Gaming
	Counter Logic Gaming		2
	Team Liquid		0