Spell Focus

Choose a school of magic. Any spells you cast of that school are more difficult to resist.

Benefit: Add +1 to the Difficulty Class for all saving throws against spells from the school of magic you select.

Special: You can gain this feat multiple times. Its e­ffects do not stack. Each time you take the feat, it applies to a new school of magic.

Source: Pathfinder Core Rulebook