A surgical end effector. A first jaw is configured to operably support a surgical staple cartridge. A lockout system is supported within the end effector and is biased laterally into lateral retaining engagement with a firing member when the firing member is in a starting position to thereby retain the firing member in the starting position. The lockout system is configured to be laterally biased out of lateral retaining engagement when contacted by a cam assembly of a surgical staple cartridge that is seated within the first jaw and the cam assembly is in the unfired position.
