Character development

How a character grows: what skill points cost, and how experience is earned faster or slower than by the character standing next to you.

Skill points

What a rank costs is decided by the class you are taking at that level, not by your best class. A skill that is a class skill for the level you are taking costs 1 skill point per rank; any other skill costs 2. A Fighter taking a level of Wizard pays 2 points per rank of Discipline at that level, and 1 point again at the next Fighter level. Ranks already bought are never lost.

You do not have to spend the points when you get them. Unspent points carry over to later levels without limit, and are spent at the cost of the class taken at the level you spend them.

Experience

Two separate things change how fast you earn.

Your favored class. A character whose levels are all in its race's favored class earns +5% experience, or +10% if the race is one of the ones that costs tokens. The bonus ends the moment you take a level of any other class. A race whose favored class is "any" gives no bonus. Some races favour a different class for male and female characters - see Races.

The multiclass penalty is separate from the favored-class bonus. Two of your base classes more than 1 level apart, with neither of them your favored class, cost you 20% experience. Two such pairs cost 40%. Prestige classes are not compared, so taking one never triggers the penalty.

Extra levels. Some races count as 1 or more levels higher than they are for anything that measures your level, experience included, so they level more slowly. Each race page states its own.

Pure class

Some abilities pay more to a character who is pure in a class. What counts as pure:

A base class: all 40 levels in it.
A prestige class: 30 levels in it, on top of the 10 base-class levels every build starts with.
Any level in another class breaks it, God's Eye Scout included.
Dropping from level 40 to 39 does not remove it: 39 levels (29 for a prestige class) count at level 39.
One check is made against your current level instead: a pure Fighter or Rogue of any level raises the level cap of their henchmen by 10.

What being pure gives each class is on that class's page, and the spell DC bonus is on Magic.

Your major class

Several systems ask which class is yours rather than what you have levels in - the on-hit save DC of an item set is the clearest case. The answer is the class you have the most levels in, and a prestige class wins a tie. If that still ties - two prestige classes, or two base ones - the class you took first counts.