Attack Rating

Attack Rating, displayed on the Character Screen, determines the percentage chance that you will hit the target, as well as the chance of the targeted monster hitting the player. If your Attack Rating is too low, you will notice that your attacks often miss. The chance to hit increases if you are at a higher character level than the monster you're attacking. Your Attack Rating can be improved by increasing your Dexterity, and by equipping magic items that specifically increase your Attack Rating.

In Diablo III, Attack Rating no longer exists; the chance to hit is always 100%, modified only by chance.

Attack Rating should not be confused with Attack Rate, better known as Attack Speed.

Diablo I/Hellfire
Attack Rating made its debut in Diablo/Hellfire in the form of To-Hit %. This chance starts at a base of 50%, and is increased by 1 for every 2 points allocated into Dexterity for melee/ranged attacks. For spellcasting, the formula changes to use Magic instead of Dexterity. There are also affixes on Weapons and Jewelry that increase that To-Hit chance further, although the best of those are only available on the former.

In addition, all heroes have 'hidden bonuses' to that To-Hit %. These bonuses are not shown, and new players may not even be aware of them until much later in the game, or even until told so by experienced players. These hidden bonuses affect the heroes greatest at their specialized form of combat- that is, to say: This being said, at max level, every hero will have up to a +70% increased To-Hit that is not seen on the character sheet. This makes it so they can focus on affixes that give both To-Hit and damage dealt, without problems due to a lack of To-Hit %.
 * Warriors and Monks have the greatest To-Hit bonuses to melee attacks, and none in spellcasting.
 * Rogues possess the highest To-Hit when using bows, and have some mediocre bonuses for melee and spellcasting.
 * Sorcerers have the highest To-Hit bonuses with spellcasting, but none in melee combat.
 * In addition, all heroes, regardless of whatever type of combat they use, earn a bonus equal to their level to their To-Hit %.

Diablo II/Lord of Destruction
Attack Rating changes form in Diablo II/Lord of Destruction. Instead of a flat % chance to hit enemies, your Attack Rating is simply another number that determines the % chance of hitting a monster. Dexterity adds to Attack Rating at 5 units per 1 point. Attack Rating affixes from gear are varied a bit more now, with flat increases, and then affixes that also add a % bonus to your Attack Rating.

Those are not all the affixes that dedicate themselves to boosting your chances to hit your target, however. Certain items, like Eaglehorn, possess a powerful affix that completely negates the defense of many monsters. And there are affixes that either negates a % of defense, or lowers the targets' defense upon a successful hit.

In multiplayer, it should be noted that the actual chances to hit a monster may appear to be much lower than what is displayed on the character sheet. This may be due to multiple reasons including server lag which results in your character being too far away from the monster (in the case of melee attacks) to properly connect with his attacks. Confirmation of this effect can be seen in crowded environments (Arcane Sanctuary and Maggot Lair notably) where on one player's screen compared to another, characters occupy different locations. Using a melee attack like smite (which always hit) and still missing also indicate that the target is out of range. Moving away then re-engaging the target usually re-evaluates the character's position and may fix the issue.