A vision sensor mounted on a robot to detect surrounding objects is discussed. Its mounting position and orientation must be identified, resulting in an extrinsic calibration problem. The author presents three classes of extrinsic calibration procedures. All use closed-form solutions. The class A calibration procedure requires a reference object at a recalibrated location. The class B calibration procedure takes advantage of robot mobility. It requires a reference frame, but not precalibration. The class C procedure, by taking full advantage of both robot mobility and dexterity, requires no reference object but the simplest one-a visible point. In simulation studies, the class A, B, and C calibration procedures have produced estimates successfully converging to true extrinsic parameter values. Results of field experiments carried out for class B and C calibration procedures are presented. For comparison, two existing B-type calibration methods have also been tested with real data. >