The Champions League group stage comprises eight pools of four teams: consequently, a team from each pot is drawn and placed into one of the eight groups available. This is done by pot and not "one at a time": that is to say, all the teams from pot one will be placed into a group, and then pot two, and so on down to the fourth and final pot.
There are some restrictions, though. Teams from the same national association cannot be drawn together, and even prior to that there will be two 'sets' of groups decided for the purpose of television rights. For example, the four teams from Spain cannot all be drawn in the same set.
* Replacement for Fenerbache, who has been removed from the competition