Abstract: An automatic machine that holds, inflates, then securely knots ordinary latex party balloons without using accessories includes a filling nozzle, surrounding clamps, and a balloon neck stretcher. Two closable jaws can be raised, lowered, advanced, retracted and twisted about the stretched neck so that a knot is formed in the stretched neck prior to release of the balloon. Mechatronics techniques make the required motions. An optional supply mechanism pre-mounts balloons on rows of nozzles on parallel sliding strips, so that a particular strip can be selected and moved to cause inflation and knotting.