Abstract: A self-locking window operator has a reversible rotary drive shaft connectable in sequence to separate linkages respectively controlling movement of a casement relative to a surrounding frame and actuation of a fastening mechanism for releasably securing the casement when closed. The drive shaft is coupled by a worm gear to a drive input member rotatable about a drive axis and each linkage has a drive output member rotatable about separate axes offset from the drive axis. The input member has a drive pin co-operable with a respective pin receiving recess of each output member for sequentially operating the linkages.