Lightner double' is conventional double in bridge used for directing the opening lead against slam contracts. It was devised by Theodore Lightner.

The Lightner double is always performed by the (to-be)dummy's LHO, directing the partner to choose an unusual opening lead. The opening lead is often a crucial trick in a deal, and it can be the last chance for the defenders to collect needed tricks. The doubler will most often have a void in a side suit, or sometimes AQ or KQ in the suit bid by the dummy. The partner is expected to find the correct lead, which might be unusual from his viewpoint; in any case, he should not lead a trump or any suit previously bid by defenders (if any).