A tool holder 1 for use as a surgical assistant. Tool holder 1 comprises: first and second beams 11,12； a frame 18； at least one linkage member 13,14 coupled to the beams 11,12 and frame 18； a mounting 15 to hold a tool, the mounting 15 being coupled to the beams 11,12； and a drive mechanism 20 mounted with respect to the frame 18, where the at least one linkage member 13,14 and mounting 15 are coupled to the beams 11,12 in a parallelogram configuration. Drive-mechanism 20 is configured to orient the mounting 15 to a tilt angle with respect to the frame 18 by moving first beam 11 with respect to second beam 12 and to drive a pan movement of the tool about a pan axis and also to orient the pan axis relative to the frame 18 dependent upon the tilt angle. Tool holder 1 may further comprise: brakes 191,192,193,194 to inhibit movement of at least one linkage element 13,14 relative to frame 18； at least one motor 201a,201b driving the pan and tilt movements. Another tool-holder with a frame carrying mounting shaft and a stop mechanism limiting the range of frame motion relative to the mounting-shaft.
