Progressive chess is a chess variant

Chess variant

A chess variant is a game related to, derived from or inspired by chess. The difference from chess might include one or more of the following:...

 in which players, rather than just making one move per turn, play progressively longer series of moves. The game starts with white making one move, then black makes two consecutive moves, white replies with three, black makes four and so on. Progressive chess can be combined with other variants; for example, when circe

Circe chess

Circe chess is a chess variant in which captured pieces are reborn on their starting positions as soon as they are captured, based on the following rules:#Pawns return to the start position on the same file they are captured on....

 is played as a game, it is usually progressively. Progressive chess is considered particularly apt for playing correspondence chess

Correspondence chess

Correspondence chess is chess played by various forms of long-distance correspondence, usually through a correspondence chess server, through email or by the postal system; less common methods which have been employed include fax and homing pigeon...

 using mail

Mail

Mail, or post, is a system for transporting letters and other tangible objects: written documents, typically enclosed in envelopes, and also small packages are delivered to destinations around the world. Anything sent through the postal system is called mail or post.In principle, a postal service...

 or some other slow medium, because of the relatively small number of moves in a typical game.

Rules

There are two main varieties of progressive chess: Italian progressive chess and Scottish progressive chess (otherwise known as Scotch chess). The two have the following rules in common:

• A check must be escaped from on the first move of a series--if this cannot be done, it is checkmate and the game is lost.
• En passant
  En passant
  En passant is a move in the board game of chess . It is a special pawn capture which can occur immediately after a player moves a pawn two squares forward from its starting position, and an enemy pawn could have captured it had it moved only one square forward...
  
  captures of pawn
  Pawn (chess)
  The pawn is the most numerous and weakest piece in the game of chess, historically representing infantry, or more particularly armed peasants or pikemen. Each player begins the game with eight pawns, one on each square of the rank immediately in front of the other pieces...
  
  s are allowed if the pawn in question moved two squares in one move, but no further, at some point during the last turn, but the capture must be made on the first move of a series.
• If ten consecutive turns are played with no captures and no pawn moves, then the game is declared a draw unless one of the players can force a checkmate (this is the progressive chess equivalent of the fifty-move rule in orthodox chess).
• If at any stage a player has no legal moves but is not in check, the game is a draw by progressive stalemate
  Stalemate
  Stalemate is a situation in chess where the player whose turn it is to move is not in check but has no legal moves. A stalemate ends the game in a draw. Stalemate is covered in the rules of chess....
  
  .

Italian and Scottish progressive chess are distinguished by rules on when a player is allowed to give check:

• Scottish progressive chess: check may be given on any move of a series, but a check ends the series--all further moves that would otherwise be allowed are forfeited. This has no effect on the other player's next series--he will receive as many moves as he would have had the other player played his full series.
• Italian progressive chess: a check may only be given on the last move of a full series (for example, on move six, a check can only be given on the sixth move)--giving a check at any other point in a series is illegal. In particular, if the only way to escape a check is to give check on the first move of the series, then the game is lost by the player in check by "progressive checkmate".

Progressive chess, like orthodox chess, is notated with algebraic notation

Algebraic chess notation

Algebraic notation is a method for recording and describing the moves in a game of chess. It is now standard among all chess organizations and most books, magazines, and newspapers...

. However, the numbering of moves is handled slightly differently. Rather than one white and one black move being given under each move number (leading to notation in orthodox chess like 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6), each turn by each player is given its own move number (leading to notation in progressive chess like 1.e4 2.e5 Nf6 3.Bc4 Qh5 Qxf7#). In this way, the move number is equal to the number of moves in a series available to a player on that turn.

Other variations

There is another form of progressive chess, English progressive chess, which makes quite a significant change to the rules: within each turn, no piece may be moved twice until every other piece which has a legal move has moved once; no piece may move three times until every other piece which can have moved twice; and so on. These restrictions do not carry over from one turn to the next--so the opening 1.e4 2.e6 f6 3.e5 Nf3 Bc4 is legal (white's e-pawn may move again because its moves are on different turns), but the sequence 1.e4 2.e6 f6 3.e5 Ba6 Bxb7 is not (the bishop has made two moves, but there are many other white pieces which have not moved on that turn). There is no en passant capture under English rules, and rules on checks follow the Scottish rules.

Progressive Take-All uses the same rules as Progressive chess, but involves capturing all pieces of your opponent's instead of checkmate. Pawns can also be promoted to Kings.

In Logical progressive chess (by Paul Byway, Variant Chess 18, automne 1995) there's no castling or pawn two advance (hence no en-passant capture) since these rules were added to speed up the game, which is not relevant in progressive form.