Canon:Race

The worlds of dungeons and dragons contain multiple races. In general, each race grants racial abilities and may modify ability scores.

Races With Ability
In earlier editions of DnD, ability scores (notably the physical abilities) were capped based on race.

In 3e and later editions, there is no cap to ability scores based on race, but races still give modifiers to certain ability scores. These modifiers lead players to choosing specific races to go alongside certain classes and not along others. For example, a player wanting to play a barbarian would probably choose a race that gave a bonus to strength and never choose a race that gives a penalty.

Races With Class
In earlier editions of DnD, the highest level a creature can take in a class depended upon its race.

In third edition, and its revised 3.5 edition, race no longer affected maximum levels in classes, but could still be a requirement for prestige classes.. Unearthed Arcana gave two racial-based class types, bloodlines and racial paragon classes.

In fourth edition, races have no strong tie to classes, with only a few paragon paths requiring specific races.

Racism
Certain species seem to have an in-born hatred for other races represented through granted racial features. For example, dwarves have a +1 racial bonus on attack rolls against goblins in 3.5e.

Subraces
For many of the popular races, subraces exist. Dwarves, Elves, and Halflings are examples.