The Convocation is an organization of cosmic beings who have sought to acquire all the knowledge they could possibly collect throughout the universe. Their agents are beings from any race whom they feel are able to perform this task. They follow the leadership of The Empyrean, a vastly powerful being from what may possibly be another dimension or alternative universe where it may have emerged. The servants of the Convocation who assist in the gathering of all knowledge are known as the Archivists. In Azeroth, Archivists come in all forms such as the Naaru, Va'nyu.
The Convocation seems to have a very enigmatic purpose aside from its desire to collect and learn all there is to learn. This may be a desire to reach omniscience though this may not even be possible on a cosmic scale.
The Convocation literally recruits from every race that has the intellectual capacity to collect information, and if that means they simply posess simple animals and small microscopic bacterium to acquire knowledge then that is what they do. They use more sentient lifeforms to organize and collect more difficult information and they actively recruit from anyone they can use.
Within the realm of Azeroth and Outland they use anyone they can possibly find from the tiny Gnomes to the vastly powerful Eredar and Naaru, two groups normally opposed to each other, under the lust for greater knowledge, the Convocation works with them all to form an effective method to gain more knowledge.
The Convocation uses agents known as Seekers who do the majority of scouting for them.
The Empyrean is the being who is overall leader of the Convocation. The Empyrean's presence is not felt within the main universe and it is unknown where the Empyrean itself rests, or who it is. What is known is that members of the Convocation are linked to the Empyrean and obey its orders unquestionably almost to suspect that the Empyrean may possess some form of mind control over them. What is known is that the Empyrean's forces are vast and powerful but what is odd is that it does not use them in any way to attack anyone.