Magic Missile

Magic Missile is an iconic 1st level offensive Wizard spell from Dungeons & Dragons, and is literally one of the oldest attack spells in the entire history of the game. It creates one or more "bullets" of magical energy which are then launched at one - or sometimes multiple - targets. In earlier editions, it's functionally a homing attack which hits automatically, with each bullet doing a relatively small amount of damage, but with each bullet doing its own damage roll, the damage can stack up, making it useful for a surprisingly decent interval.

Since it is so low level and always hits, it pairs nicely with Metamagic to add rider effects. As it's a force effect, almost nothing in the game even resists it (epic Challenge Rating Force Dragons are the only OGL monster to do so), ensuring its low damage will almost always hit.

The spell is so iconic (and it's name so generic) that many gamers will use the name as a catch-all for any low-level "fire energy at somebody" type spells. In Warhammer Fantasy, it's even a distinctive category of attack spells. Despite its iconicity, there is almost no official art of it in official Dungeons & Dragons material. Luckily there's a LOT of art from other franchises, vidyas, and various internet drawfags, if you're looking for something cool to suit your tastes.

In Dungeons & Dragons 3rd Edition, the Force Missile Mage is a Wizard Prestige Class that specializes in taking this humble spell and pushing it to new heights.

Through the Ages

As you probably already know, Dungeons & Dragons has been around a long time, and gone through a fair few editions with fairly different mechanics each time. So, how has the humble Magic Missile fared in each edition?

BECMI

In BECMI, Magic Missile is a 1st Level Magic-User spell with a duration of 1 Round that creates a single glowing projectile of magical energy, plus two more projectiles for every 5 levels of experience the caster has (so a 6th level Magic User produces 3 missiles per casting). It has a range of 150', and each missile can target its own independent target, or be assigned to hit the same target. The target is automatically struck, with no saving throw, and takes 1d6+1 damage per missile that hits them.

AD&D

In the very first edition of Advanced Dungeons & Dragons, Magic Missile was expanded. Still a 1st level Magic-User spell, it now has a range of (6' + 1'/level), a Duration of "Special", an Area of Effect of "one or more creatures in a 10 foot square area", Vocal and Somatic spellcasting components, a Casting Time of 1 Segment, and No Saving Throw. It also was officially declared to be part of the new "Invocation/Evocation" school of magic.

When cast, this version of the spell creates one magical missile, plus another missile per 2 levels of experience. Each missile can be targeted at either the same creature or a different creature, so long as they are within the aforementioned range of area of effect, and targets take d4+1 damage per missile that strikes them.

Come second edition, and the spell was reprinted, with only a few changes. Firstly, it was specified that the caster must be able to clearly detect and identify a target before they can blast them with a magic missile, so near-total concealment protects you from the spell. You also cannot single out specific body parts, and the spell does no damage to inanimate objects, so you can't use magic missile to shoot out a lock. Distance is now (60 + 10/level) yards instead of feet. Finally, the number of possible missiles was now capped at 5 per casting from 9th level - which was quite an nerf, considering that, Rules As Written, the BECMI version could give you fifteen missiles and the AD&D 1e version could give you ten.

3e

Since 3e largely tried to market itself as a polished revamp of 2nd edition, a lot of the underlying mechanics of the 3e magic missile are identical to its 2e counterpart; it's now a 1st level Evocation spell available to Wizards and Sorcerers. It takes 1 standard action to cast, requires Vocal and Somatic spell components, and has a Medium range, which is specified as 100 feet + 10/level feet. It has an Instantaneous duration, grants no saving throw but can be resisted, and can target up to 5 creatures, no two of which can be more than 15 feet apart. It still only creates 1 missile, plus one per two caster levels, maxing out at 5 missiles, and each missile only does 1d4+1 damage, which is now specified as being "Force type" damage. You still can't target specific body parts or use it to damage inanimate objects.

4e & Essentials

Despite the changes that the Wizard underwent in this edition, the trusty Magic Missile remained. Now a Level 1 At-Will Attack spell, it takes a standard action to use the spell. It has the Keywords "Arcane", "Force" and "Implement", and targets one creature within a range of 20 squares (100 feet); for the first time, a creature can potentially dodge a Magic Missile, as it now uses an Intelligence vs. Reflex attack roll. On a hit, it does 2d4 + Int modifier Force damage, which increases to 4d4 + Int modifier Force damage at 21st level. It has the special rider that it counts as a Ranged Basic Attack, so any effect or power that lets the Wizard use a Basic Attack lets them cast Magic Missile.

Essentials offered an alternative version of the Magic Missile in its "Heroes of the Fallen Lands". This version is still an At-Will 1st Level Attack spell, with a Range of 20 Squares and taking a Standard Action to use. It targets one creature, adds the enhancement bonus from the caster's implement (if any) to damage inflicted, and can be used as a ranged basic attack. But it now hits automatically... at the cost of doing incredibly piddly damage; 2 + Int modifier! This base damage increases to 3 at 11th level and to 5 at 21st level but, yeah, most fans of 4e pretend this version never existed.

5e

The most recent iteration of the Magic Missile is once again a 1st level Evocation spell. It takes 1 action to cast, it has Vocal and Somatic spell components, it has an Instantaneous duration, and it has a range of 120 feet. It creates 3 darts of magical energy (+1 per spell level over 1st if upcast), which can be directed at any number of targets within the range, or all sent after the same foe. The target(s) take 1d4+1 Force damage per missile that hits them.