Eleusis is a multi-genre card game. It technically belongs to the shedding group and inductive group.

In this game players try to get rid of their cards by playing them to a discard pile. However, the unique feature of this game is that the rule governing which cards can legally be played is initially unknown to the players. The dealer (sometimes known as "God") secretly invents and writes down the rule governing play. The other players try to guess the rule by observing which plays are legal.

The original version of Eleusis was invented by Robert Abbott in 1956, and was published in Martin Gardner's column in the Scientific American in June 1959. It subsequently appeared in Gardner's 2nd Scientific American Book of Mathematical Puzzles and Diversions and in Abbott's book Abbott's New Card Games (Stein & Day 1963). It was named after Eleusis, the home of the Greek Eleusinian Mysteries cult.

In the 1970s Abbott made some major improvements to Eleusis, including the option for a player to become a prophet and try to predict whether each play would be called legal or illegal. This current version, The New Eleusis, was published in the Scientific American in October 1977. There is also a booklet about it, obtainable from the inventor, which gives a fascinating account of the development of the game, as well as the rules.

The game is sometimes considered an analogy to the problems of scientific method. It can be compared with the card game Mao, which also has secret rules that can be learned inductively. The games of Penultima and Zendo also feature players attempting to discover inductively a secret rule or rules thought of by a "Master" or "Spectators" who declare plays legal or illegal on the basis of the rule(s).