Shielded Mage (Combat, Shield Mastery)Source Armor Master's Handbook pg. 19
You have learned how to cast spells from behind the safety of a shield.
Prerequisites: Shield Focus, base attack bonus +3 or fighter level 1st.
Benefit: You reduce the arcane spell failure of any shield you use by 15% (to a minimum of 0%). Using a shield does not prevent you from completing somatic spell components with the hand wielding the shield.