- For general information about demonology, see Demonology.
Overview
- Main article: Warlock talents#Demonology
Demonology is the second of the Warlock's three talent trees. It is centered around improving the Warlock'sminions, Stones, Stats and survivability as well as the warlock's two armor spells. The key talents include 
[Summon Felguard], 
[Soul Link], 
[Demonic Knowledge] and 
[Master Demonologist]. It is often taken at mid levels (40+) for Demonic Knowledge which provides a substantial increase in damage before much gear with +spelldmg is available.
Advantages
A Demonologist has larger health and mana pools, pets which deal more damage and can soak up more as well access to the infamous Felguard minion, which can be used as a DPS tank, DPS or offtank.
Demonologists have a much higher +spelldmg than other Warlocks due to [Demonic Knowledge] and 
[Demonic Aegis].
Demonologists are a viable tree to solo train in with talents such as [Soul Link] and 
[Demonic Resilience] improving the tanking ability of the warlock's active pet, as well as reducing damage taken by both demon and master.
Due to the large amounts of spell resistance granted by the [Master Demonologist] effect of the Felhunter minion, as well as the large amounts of life a demonologist has (on par with warriors and paladins, if not higher though not having nowhere near as much damage mitigation), they are arguably the best caster tanks and are able to generate threat using Searing Pain. This also makes them the best anti-casters along with the Felhunter's 
[Devour Magic] and 
[Spell Lock] abilities.
Demonologist's stones, if they decide to spec into those talents, are more powerful. The 
[Healthstone] which is in effect an extra potion, on a different timer which can be traded as well as the Healthstones generated from Ritual of Souls heal significantly more helping in raids; the 
[Firestone] provides more fire spell damage as well as dealing more on a melee proc (though the Warlock should avoid melee combat when possible) and the 
[Spellstone] provides more spell critical rating. Though the latter 2 stones become less useful as wands with better stats emerge at higher levels, they are good talents for solo training.
[Master Demonologist] and 
[Demonic Sacrifice] give the Warlock a high grade of flexibility, offering multiple different effects, depending on the active or sacrificed pet.
Some 5 man instances could be tanked with a Voidwalker or Felguard if a tank is unavailable. However even non-protection specced warriors tank much better than a warlock minion.
Disadvantages
If a Demonologist's pet dies, their DPS is greatly reduced, much like a Beast Mastery Hunter.
Limited talents for mana effeciency and DPS improvement.
There are no threat management talents in the whole tree.
Raiding with a demonologist build is very situational, with encounters requiring a caster tank being the main viable use. AoE heavy encounters will most likely lead to a dead pet greatly decreasing damage output and survivability. The felguard might possibly survive with its high life and Avoidance (pet).
There is limited party/raid synergy with less or no access to talents such as Malediction and Shadow Embrace in the affliction tree.
Even with talents summoning minions takes a rather large amount of mana and takes a long time, 
[Fel Domination] is on a 15 minute cooldown. Having to resummon a minion in battle is not very practical unless Fel Domination is available.
Other Notes
One of the best tricks of the Demonology specialized Warlock is to use the Voidwalker's Sacrifice ability and then use [Fel Domination] combined with 
[Master Summoner] to summon a new minion in half of a second.
After release, it was looked down upon as not being useful, though this opinion is not as prevalent since the addition of [Master Demonologist]. More recently though, there have been calls by some that Demonology Specialized Warlocks need to be nerfed due to their increased survivability due to the Soul Link talent. However, since then, the Warlock class, and especially its Demonology tree, has undergone major changes.
See also
Affliction | Demonology | Destruction