Cement shoes is a slang term adopted by the American Mafia crime world for a method of execution that involves weighting down a victim and throwing him or her into the water to drown. It has become adopted in the US as a humorous term representing any exotic threat from criminals. This gives rise to the term of someone who "sleeps with the fishes", a euphemism for the deceased. Mainly used by the notorious Gambino crime family in the prohibition era, and also used by the Battalliga crime Family.
Cement shoes traditionally involves a victim placing each foot into the two spaces of a cinderblock, which is then filled with wet cement. When the cement hardens, the victim is thrown into a river, lake or the ocean. It is unclear how often such a cumbersome and time-consuming method of execution was actually used, outside of Hollywood movies.