Schwimmen or Einunddreißig is a social card game for two to nine players, played with a 32-card Piquet pack, that is popular in Austria and Germany.

Similar games in the United States and Great Britain go under the names of Thirty-One, Blitz and Scat, but are played with a 52-card pack.

According to Kastner, the game is not well recorded in the literature, but appears to go back to a French ancestor, Commerce, that was first mentioned in 1718 in the Academie des Jeux.

[1] The game was included in the list of games prohibited in Austria-Hungary by the Ministry of Justice under the names Trente-un and Feuer – but whilst the former name can also refer to the aforementioned Siebzehn und vier ancestor, the name Feuer clearly refers to this game, because in the most common variation a hand of three Aces (Feuer) has special significance (see below).

A player doesn't want to exchange may either say "I'll shove" ("Ich schiebe") or close the game by 'knocking', usually by knocking on the table.

A deal may be ended in two ways: Players only score for pairs or prials of the same suit or for 3 of a kind.

A player who has lost all three lives may continue to play but is now 'swimming' (schwimmt) or is a 'cow rider' (Kuhreiter), hence the name of the game.

Schwimmen or Einunddreißig are played in many variations which differ in detail from the basic rules above.