A multiple pig launcher includes a tubular structure along which a series of pipeline pigs may be advanced in stepwise fashion to be launched into a pipeline in succession. A launching station holds a first pig at a downstream end of the series in readiness for launch. A pig stopper mechanism is operable selectively to hold a second pig at a holding station upstream of the launching station when launching the first pig and to release the second pig from the holding station to be advanced into the launching station after the first pig has been launched. The pig stopper mechanism comprises at least one radially movable gripper element that can apply radially inward gripping force to a pig held at the holding station.