Spell Focus

Spell Focus [General]

Choose a school of magic, such as illusion. Your spells of that school are more potent than normal.

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: Player's Handbook