The Blackmar–Diemer Gambit (or BDG) is a chess opening characterized by the moves: 1. d4 d5 2. e4 dxe4 3. Nc3 where White intends to follow up with f2–f3, usually on the fourth move. White obtains a tempo and a half-open f-file in return for a pawn, and as with most gambits, White aims to achieve rapid and active posting of their pieces in order to rapidly build up an attack at the cost of the gambit pawn. It is one of the few gambits available to White after 1.d4. History The Blackmar–Diemer Gambit arose as a development of the earlier Blackmar Gambit, named after Armand Blackmar, a relatively little-known New Orleans player of the late 19th century who popularized its characteristic moves (1.d4 d5 2.e4 dxe4 3.f3) and was the first player to publish analysis of the opening. The popularity of the original Blackmar Gambit, however, was short-lived, as it was basically unsound, allowing Black to secure a superior position after White's immediate 3.f3 with 3...e5!. In 1889, Ignatz von Popiel came up with the idea of 3.Nc3, though his main idea was to meet 3...Nf6 with 4.Bg5 (rather than the more usual 4.f3) and provided analysis of the Lemberger Counter-Gambit (3.Nc3 e5). The evolved, modern form of this gambit owes much to the German master Emil Josef Diemer (1908–1990), who popularized the continuation 3.Nc3 Nf6 and then 4.f3 (when 4...e5? is ineffective as 5.dxe5 hits Black's knight, and after 5...Qxd1+ 6.Kxd1 the knight has to retreat to d7 or g8). The position resulting after 3... Nf6 4.f3 reflects the main line of the gambit accepted, although other Black responses on move three are possible. After many years of analysis, Diemer wrote a book on the opening in the late 1950s, titled Vom Ersten Zug An Auf Matt! (Toward Mate From The First Move!), with most of the published analysis devoted to the Ryder Gambit (and associated Halosar Trap), a double-pawn sacrifice characterized by the moves 4...exf3 5.Qxf3. Assessment This gambit is considered an aggressive opening, but its soundness continues to be the subject of much debate both on and off the chessboard. Dismissed by many masters on the one hand, and embraced enthusiastically by many amateurs on the other, many consider that Black has good chances of defending successfully and converting the extra pawn in the endgame, while theory suggests that Black has many ways to . As