Abstract: A manipulator comprises three arms 1 which can pivot at different points on a supporting structure 6 and which can be driven longitudinally to adjust their effective lengths. The longitudinal axes of the three arms intersect at a common point but their lower ends are offset from this point and are pivoted about respective axes which also intersect at the aforementioned common point. They are pivotted to an end effector mounting flange 8 which optionally comprises a fourth arm 11 which slides and pivots on the supporting structure. The fourth arm serves to ensure that the flange 8 always faces at a known orientation. It can also be used in co-operation with suitable sensors to produce signals on lines 15, 16 and 18 to a control unit which drives the arms 1 in their linear directions.