The 2015 edition of ESL One Cologne is now underway, with 16 top-ranked Counter-Strike: Global Offensive teams battling in the Group Stage for entry into the quarterfinals. Four teams will make the move today, and another four will advance on Friday.

The teams in competition are divided into four groups: Group A features Team SoloMid, Ninjas in Pyjamas, Renegades, and Counter Logic Gaming; Group B contains Team EnVyUs, Luminosity Gaming, Team Kinguin, and FlipSid3 Tactics; Group C has Fnatic, Natus Vincere, Titan, and Team eBettle; and Group D boasts Virtus.Pro, mouseports, Cloud9, and Team Immunity. On Friday, the groups will be redrawn for eight more Decider/Elimination matches.

Right now the favored teams are perpetual champions Fnatic followed by Team SoloMid, a team formed in February that hasn't yet won a major.

ESL One Cologne is also interesting this year because, for the first time ever, ESL will conduct randomized drug testing during the competition. The move comes in response to a claim by former Cloud9 player Kory "Semphis" Friesen that he and his teammates were on Adderall at ESL One Katowice.

The real action will begin on Saturday, with the first quarter-final match scheduled to begin at 4:45 am EDT. Semi-final matches are slated for 5:45 and 9:10 am EDT on Sunday, followed by the big finish at 1 pm EDT the same day. Follow all the action at esl-one.com.