Summons

Many characters in DDO can conjure an ally to help them in their endeavors. A summoned creature appears where you designate and acts immediately, and it attacks your opponents to the best of its ability. You can only have 1 summoned creature of any type serving you at a time. Summoning a new creature of any type will return the previous one to its home plane.

The summoned creature cannot be given orders nor use ladders, climb walls, or jump off platforms, but will generally follow you and even teleport if you move far enough away. It can be affected by beneficial and detrimental spells much like any Hireling or party member. It's often more efficient spell-points wise to summon a new creature than to heal an existing one.

Duration
There is no spell timer shown on screen, so you have to figure out yourself how much summoning time remains. Most summoning spells have a maximum duration of 10 minutes (exceptions noted below). Summoned creatures don't disappear when you rest. They vanish if the you die or leave the instance. You cannot dismiss a creature.

Summons vs. hirelings / companions / ...
The following creatures count as summoned and are subject to the restriction of a single summoned creature simultaneously:
 * Creature summoned via spell / effect
 * Racial Enhancement Defender
 * Undead created via Create Undead

In addition, you can have all of the following:
 * an Artificer Iron Defender pet OR a Druid Wolf pet
 * a Pale Master undead pet
 * a Favored Soul Archon
 * a Friend of Nature - Primal Avatar minor pet
 * one or more charmed creatures
 * one or more Hirelings
 * one summoned creature per hireling
 * a cosmetic creature companion

Improving summons
All of your personally summoned / charmed creatures and hirelings can be enhanced by the following feats / class features / epic destinies:
 * Augment Summoning feat (also on )
 * Past Life: Druid feat
 * Druid enhancements, such as Druid Blood Moon Frenzy I
 * Primal Avatar abilities, such as Natural Shielding
 * Magister's Grand Summoner ability

Additionally, summons benefit from buff spells / abilities, just like any party member.

Summoning spells

 * Summon Monster I to IX: Clerics, Favored Souls, Sorcerers, Wizards, Bards (I-VI)
 * Summon Nature's Ally I to IX: Druids, Rangers (I-IV)
 * Flame Turret: Artificers - 1 minute duration instead of the usual 10 minute of most summons
 * Create Undead: Clerics, Favored Souls

Clickies

 * - Summon Monster II
 * - Summon Monster III
 * - Summon Monster III
 * - Summon Monster III
 * - Summon Monster III
 * - Summon Monster IV
 * - Summon Monster IX
 * - Summon Monster IX
 * - Summon Unknown Monster - random from a list of 4 monsters, CR1-6
 * - Summon Unknown Monster II - random from a list of 4 monsters, CR10-16
 * - Summon Xoriat Horror - random from a list of 4 monsters, CR13-16 - 5 minute duration instead of the usual 10 minute of most summons
 * - Epic Thaarak Hound, CR35 - 5 minute duration instead of the usual 10 minute of most summons
 * Tier 2 Green Steel - Dense Stone Earth Elemental, CR12 - 5 minute duration instead of the usual 10 minute of most summons

Consumables

 * Scrolls:
 * Summon Monster I to VII can be purchased from vendors or found in chests; VIII and IX can only be found in chests
 * Summon Nature's Ally I to IX do not exist as scrolls
 * Flame Turret can only be found in chests
 * Create Undead can only be found in chests
 * Elemental Gem (Earth) - Medium Earth Elemental (Summon Monster V)
 * - Summon Monster VII
 * Gem of Freezing Tides - Greater Ice Mephit (Summon Monster IV)
 * Gem of Ocean's Winds - Air Mephit (Summon Monster III)
 * Greater Gem of Freezing Tides - Large Water Elemental (Summon Monster VI)
 * Greater Gem of Ocean's Winds - Greater Air Elemental (Summon Monster VIII)

Epic Destinies

 * Summon Dryad Elder - Primal Avatar Tier 4
 * Energy Vortex - Draconic Incarnation Tier 6
 * Call Kindred Being - Magister Tier 4