As player characters overcome challenges, they gain experience points (also called “XP”) as a quantification of everything they’ve learned and practiced. As the PCs attain more experience points, they advance in character level, gaining new and improved abilities at each level. Characters advance in character level (or “level up”) when they earn specific amounts of experience points—the Experience Point Total column of Table 2–4: Character Advancement shows the experience points needed to reach each level. Typically, leveling up occurs at the end of a game session, when your GM awards that session’s XP, or between the end of that session and the start of the next.

The process of advancing a character works in much the same way as generating a character, except that your previous choices concerning race, ability scores, class, skills, theme, and feats cannot be changed. Adding a level generally gives you new class features; additional skill ranks to spend; more Hit Points, Stamina Points, and Resolve Points; and possibly an additional feat or theme benefit, or even extra ability points (see Table 2–4: Character Advancement).

Follow the steps below to advance your character.

Step 1: Apply Any Ability Increases

Every 5 levels, you get to increase and customize your character's ability scores. Each time he reaches one of these level thresholds (5th, 10th, 15th, and 20th—see Table 2-4), choose four of his ability scores to increase. If a chosen score is 17 or higher (excluding ability increases from personal upgrades), it increases permanently by 1. If it's 16 or lower, it increases by 2. You can't apply more than one of these increases to the same ability score for a given level. Unlike during character creation, ability score increases gained from leveling up can push your character's ability scores above 18.

If an ability score increase results in a change to an ability modifier, don't forget to adjust any statistics that rely on that modifier, such as attack bonuses, saving throws, total skill bonuses, Resolve Points, Stamina Points, and the DCs of class features and spells. Note that ability score increases are effective retroactively; when your character's ability score increases, it increases his total number of ability-based statistics—things like Resolve Points, Stamina Points, or skill ranks—as if he had the higher value at previous levels as well. For example, a mechanic with an Intelligence score of 17 has a modifier of +3, and thus gets 7 skill ranks to spend at each level. If at 5th level he increases his Intelligence score to 18, he’ll have a modifier of +4, and thus get 8 skill ranks to spend from this level forward—but he’ll also get 4 additional ranks to assign, reflecting the ranks he would have received if he’d had an Intelligence score of 18 at his first 4 levels.

Step 2: Add New Class Features

Your character's can either advance to the next level of his current class or take a level in a different class (see Multiclassing below). Increase your character's Hit Points by the number that his class grants him, increase his Stamina Points by the amount specified in the class plus his Constitution modifier, adjust his saving throw and attack bonuses, and integrate the class features he gains at that level (including choosing any new spells he has gained if he's a spellcaster). In addition any new class features he gains, some class features he received at lower levels may improve at higher levels, so be sure to check whether his existing class features have gotten better.

Step 3: Add New Feats or Theme Benefits

Your character gets a new feat at every odd-numbered level. This is in addition to any bonus feats he might get from his class. When choosing a new feat, be sure to check the prerequisites to make sure your character qualifies for it.

Your character gains a new benefit from his theme at 6th level, 12th level, and 18th level.

Step 4: Invest Skill Ranks

Whenever your character levels up, he gains a number of new skill ranks based on his class and his Intelligence modifier; as noted in Step 1, he may also gain skill ranks as a result of his Intelligence modifier increasing. Invest these new skill ranks in skills (he can invest in existing skills or new skills), keeping in mind that his ranks in any one skill can't exceed his character level. If any of his ability score modifiers increased in Step 1, don't forget to adjust those bonuses to his skill checks.

Multiclassing

Most characters continue to advance in their chosen classes for their entire careers, gaining ever more impressive abilities. Sometimes, however, you might want your character to crosstrain and pick up some of the abilities of a different class. When such a character levels up, instead of gaining the next level of his existing class, he can add a level of a new class, adding all the 1st-level class features of that class to his existing class features. This is referred to as “multiclassing.”

For example, let's say a 5th-level soldier decides to dabble in the magical arts and adds 1 level of technomancer when he next advances in level (such a combination of levels is commonly written “soldier 5/technomancer 1”). Such a character retains the class features and abilities of a 5th-level soldier—his bonus feats, style techniques, armor and weapon proficiencies, and other class features—but also gains the class features and abilities of a 1st-level technomancer, such as the ability to cast 1st-level technomancer spells and the technomancer's spell cache class feature. He adds all of the Hit Points, Stamina Points, base attack bonuses, and saving throw bonuses from the 1st-level technomancer on top of those gained from being a 5th-level soldier, and is still considered a 6th level character (his character level is 6th.)

It's important to keep track of which effects and prerequisites rely on a character level versus class level. For example, feats might require a minimum class level or character level, while almost all class features are based on the character's level in the class that grants that feature. Casting spells is an exception—when determining caster level, a character adds together his levels from different spellcasting classes (such as mystic and technomancer).

A multiclassed character can have more than one key ability score. For each class, your key ability score remains the same as normal for that class (and for the class features that rely on that score). For any key ability score calculation not tied to class, such as determining your maximum Resolve Points, use whichever key ability score has the highest value (and therefore the highest modifier).

You can take as many levels of as many different classes as you want, but while it might seem tempting to be a dilettante, spreading yourself thin comes with a cost. Since you always start at the ground floor with a new class, it's easy to end up with a bunch of low-level abilities that can't compete with the higher-level abilities of a single-class character of the same level. For instance, an envoy 3/soldier 4/technomancer 3 may be well-rounded, but she's going to get stomped into pudding by a 10th-level soldier, and she will be consistently outperformed by the other 10th-level characters in her party.

Retraining

In general, decisions made about your character when leveling up are permanent; you can't go back and change his ability scores, feats, skills, and so forth later on. For characters who desperately want to change their past and replace abilities, however, there is a technological solution: the mnemonic editor, a device by which old knowledge and abilities can be edited out of your character's brain and permanently replaced with new ones, thus allowing you to partially rebuild your character—with your GM's permission, of course.