A surgical instrument that includes an instrument shaft having proximal and distal ends, a tool disposed from the distal end of the instrument shaft, a control handle disposed from the proximal end of the instrument shaft, a distal motion member for coupling the distal end of the instrument shaft to the tool, a proximal motion member for coupling the proximal end of the instrument shaft to the handle, actuation means extending between the distal and proximal motion members for coupling motion of the proximal motion member to the distal motion member for controlling the positioning of the tool and a locking mechanism for fixing the position of the tool at a selected position and having locked and unlocked states.