Spanish Game / Ruy Lopez

3. Bb5 is known as the Ruy López opening or Spanish game. White threatens to trade off Black's c6 knight, the defender of e5, so indirectly threatens to win the pawn, though it's not an immediate threat because of a tactical trick where Black can win the pawn back.

White is playing for quick development (they are ready to castle already) and control of the centre. They'd like to eventually play c3 and d4 to build a pawn majority in the centre.

Black can respond in a variety of ways. The most common continuations are 3...a6 and 3...Nf6.

3...a6, the Morphy defence, forces White to make a decision about the bishop: retreat, or exchange. The oldest continuation is to take the knight, 4. Nxc6, the Exchange variation. This doesn't win the e5 pawn, however (4...dxc6 5. Nxe5? Qd4! and Black can win the pawn back). The Exchange variation is playable, but more popular is 4. Ba5, preserving the bishop pair and pressure on Black's knight. After 4. Ba5 however, Black has the option of cutting off that pressure whenever they wish with b5.

3...Nf6, the Berlin defence, is the main sideline. Recognising there is no immediate threat to their pawn centre, Black develops and threatens Nxe4 instead. The Berlin has a reputation for being solid but very drawish. The opening often leads into a quick exchange of queens and equal endgame (the Berlin Endgame) or a fast draw by repetition.

Many other moves are available, some neglecting completely the protection of the knight and the pawn and continuing development.

The two next most commons sidelines in master-level play are 3...f5!? and 3...g6.

• 3...f5!?, the Schliemann or Jaenisch gambit, is a sharp line where Black attacks White's centre from the flank. Accepting with 4. exf5 allows 4...e4. The usual response is 4. d3, which renews the threat of 5. exf5 because the pawn on d3 prevents 5...e4.
• 3...g6, the Fianchetto defence, prepares a king-side fianchetto, although often Black delays actually playing Bg7 until they have played d6.

In amateur games, more common sidelines are 3...Bc5 and 3...d6.

• 3...Bc5 is the Classical variation. Since there is no danger to e5 yet, Black simply develops the bishop to pressure White's kingside and the vulnerable f2 square. This is one of the oldest defences.
• 3...d6, the Old Steinitz defence, was the continuation recommended by William Steinitz. Playing 3...a6 and later b5, he reasoned, just allows White's bishop to get to where it would like to go: to man the dangerous b3-to-f7 diagonal. Steinitz advocated 3...d6 instead to defend the e5 pawn directly. However, this is passive, inhibiting Black dark square bishop, and Black self-pins their knight: White's most critical reply is 4. d4. A "Modern" Steinitz defence delays d6 until after 3...a6.

Other lines have been tried. These include:

• 3...Nd4!?, Bird's variation. Black counterattacks the bishop: after 4. Nxd4 exd4 Black has gained some space but has slightly worsened their pawn structure.
• 3...Nge7, Cozio's defence, defending the knight with the other knight.
• 3...d5?!, the Spanish countergambit. Black hopes to bamboozle White by offering them a choice of centre pawns to capture.

The earliest known analysis of this opening is from the 15th century Göttingen manuscript. The 16th century Spanish priest Ruy López de Segura analysed the opening in his 1561 book on chess, from which both the modern names Spanish opening and Ruy López derive. Ruy López de Segura considered the danger posed to Black by 3. Bb5 to be so severe that it refuted 2...Nc6, and recommended 2...d6 to Black instead.

In the 18th century, the Modenese masters Ercole del Rio and Domenico Lorenzo Ponziani analysed the exchange variation of the opening (3...a6 4. Bxc6) and concluded that the bishop was better placed on the c4-to-f7 diagonal (i.e. 3. Bc4, the Italian game).^[1]

In the mid-19th century, Carl Jaenisch published detailed analysis of 1. e4 e5 in French and English circulars. Writing "this opening has been strangely overlooked and passed by, we may say in contempt, by all writers", Jaenisch's treatment of 3. Bb5 reinvigorated interest in what he called "Lopez's Knight's Game". Jaenisch was dismissive of the defences 3...Nge7 (Cozio defence) and 3...Nd4 (what we now call Bird's defence), and especially critical of del Rio and Ponziani's analysis (which he called "very defective"). Jaenisch's treatment of 3...a6 reads as very modern:^[1]

White's correct move is simply to withdraw the attacked Bishop to [a4], preserving its menacing direction. This shows that the move, [3...a6], is absolutely useless, for if Black follow it up with [4...b5], White's Bishop is brought into a good line of attack on [b3]... We may remark in general, that the object of [3. Bb5] is not to double a Pawn for Black by taking his [Knight], but to confine the development of his right wing as long as possible; and it is precisely in order not to allow him to escape from the confinement that the Bishop, if attacked by [a6], either at the third or any subsequent move, must not take the [Knight] but retire to [a4].

This was the beginning of the modern Spanish main line. The next major shake up occurred in the 1960s when new theory in the Marshall attack, an aggressive turn 8 gambit for Black, drove White players to adopt anti-Marshall systems to avoid it.

In 2000, the main alternative to 3...a6, 3...Nf6, was repopularised when Vladimir Kramnik used it as a drawing weapon against Garry Kasparov during his successful World Championship challenge.

Nowadays the Spanish opening is known as one of the most deeply studied and popular chess openings, and one of the most frequently seen at the highest levels of chess. It is the continuation of the Open Game most commonly seen in master-level play, adopted by virtually all players at some point in their chess career.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1. e4 e5 2. Nf3 Nc6 3. Bb5

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Wikipedia has related information at Ruy Lopez

• Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.