Open Game

White's most popular first move, 1.e4, moving the king pawn two squares, immediately stakes a claim in the center and frees two pieces (the queen and king's bishop) for development. Bobby Fischer called 1.e4 "Best by test." On the negative side, 1.e4 places a pawn on an undefended square and weakens the squares d4 and f4. The symmetrical 1...e5 incurs the same strengths, but also the same drawbacks, for Black: White's usual response 2.Nf3 attacks the undefended pawn.

After having been the most common response to 1.e4 until the mid-20th century, 1...e5 remains the second most popular response to 1.e4 at the top level; 1...c5 (the Sicilian Defense) is slightly more popular among tournament players. Along with the Sicilian, it is the most extensively analyzed of Black's responses to 1.e4.

The most popular second move for White is 2.Nf3. The move attacks Black's king pawn, prepares to castle kingside, and supports playing d2-d4 in many lines. Black's usual reply to 2.Nf3 is 2...Nc6, defending the king's pawn and developing the knight. From here several named openings can arise:

• 3.Bb5, the Ruy Lopez (or Spanish Game), is White's most frequent move at the top level, and one of the most extensively played and analyzed openings at all levels of chess. Black's most common response is 3...a6, forcing White to make a decision between exchanging the bishop for the knight with 4.Bxc6 or retreating with 4.Ba4. Also common is 3...Nf6, the Berlin Defense. Black has several alternatives, the sharpest of which is 3...f5, the Jaenisch Gambit (or Schliemann Defense).
• 3.Bc4, the Italian Game, is White's second most popular move, and has been extensively analyzed for hundreds of years. It usually leads to either the Giuoco Piano (3...Bc5) or the Two Knights Defense (3...Nf6), where White may play 4.Ng5, 4.d4, or 4.d3. In the Giuoco Piano, White can play 4.c3 and 5.d4, the classical approach; 4.b4, a sharp pawn sacrifice known as the Evans Gambit; or 4.c3 and 5.d3 (also reached with other move orders), the modern approach, among various other plans.
• 3.d4, the Scotch Game, was popular in the 19th century and is still the third most common move. After the usual 3...exd4, White may either recapture with 4.Nxd4 with an approximately equal game, or play the Scotch Gambit (4.Bc4), a risky but dangerous tactical line against an unprepared opponent.
• 3.Nc3, the Three Knights Game, was also a popular move in the 19th century and is still occasionally played at the top level. Black's usual reply is 3...Nf6, the Four Knights Game. It frequently leads to positional games and is generally considered less challenging for Black to defend against than the three lines above.
• 3.c3, the Ponziani Opening, has never achieved widespread popularity but is occasionally used as a surprise weapon.

Other third moves for White such as the Konstantinopolsky Opening (3.g3) and Inverted Hungarian Opening (3.Be2) are rarely played and offer White no advantage.

After 2.Nf3, there are two frequent alternatives to 2...Nc6:

• 2...Nf6, the Petrov Defense, a popular choice at the top level. It has a drawish reputation but there are many sharp lines. The main line is 3.Nxe5 d6 4.Nf3 Nxe4; 3.d4 is a common alternative. Alternatively, White can avoid the extensive theory of the Petrov with 3.Nc3, which often transposes into a Four Knights Game with 3...Nc6.
• 2...d6, the Philidor Defense, defends the pawn on e5 but has the disadvantage of restricting the mobility of Black's king's bishop, and typically leads to solid but passive positions for Black. For this reason, it largely fell out of favor by the early 20th century as Black players sought more dynamic options, but it has a dependable reputation.

The following moves are rare and generally considered dubious:

• 2...f5, the Latvian Gambit, a risky pawn sacrifice.
• 2...d5, the Elephant Gambit, another risky pawn sacrifice.
• 2...Qe7, the Gunderam Defense, an eccentric defense which blocks the development of the king's bishop.
• 2...Qf6, the Greco Defense, is weak, exposing the queen to early attack and taking up the king's knight's natural square.
• 2...f6, the Damiano Defense, is weak and may be met by either 3.Nxe5 or 3.Bc4 with advantage for White.
• 2...Bc5, the Busch-Gass Gambit, was something of an online fad in the early 2020s. It is well met by 3.Nxe5 Nc6 4.Nf3.

White has four frequent alternatives to 2.Nf3:

• 2.f4, the King's Gambit, where White offers a pawn to undermine Black's center and achieve quick development. It was very popular before the 20th century with master and amateur alike. Black often accepts the pawn by playing 2...exf4, but there are alternatives, such as 2...d5, the Falkbeer Countergambit, which counterattacks in the center.
• 2.Nc3, the Vienna Game, which became popular for a while in the 19th century, also frequently features such attacks on Black's center by means of f2-f4, but there are multiple alternative plans, such as 3.Bc4, developing the bishop to an active square, and 3.g3, intending to fianchetto with Bg2.
• 2.Bc4, the Bishop's Opening, was also more popular in the past. It often transposes to the Italian Game or Vienna Game, but there are several independent lines.
• 2.d4 is the Center Game, in which White immediately opens up the center. After the recapture 2...exd4 3.Qxd4, Black gains a tempo by attacking White's queen with 3...Nc6. An alternative is to sacrifice one or two pawns by offering the Danish Gambit (3.c3); however, a safe practical reply for Black is to decline the gambit with 3...d5.

Other second moves are rare and do not gain any advantage against correct play:

• 2.Qh5, the Danvers Opening, also known as the Parham Attack or Wayward Queen Attack, is usually played only by amateurs, though Hikaru Nakamura has experimented with it in grandmaster tournaments.
• 2.Qf3, the Napoleon Opening, has even less to recommend it as Black can easily block any mating threats without compromising development.
• 2.Bb5, the Portuguese Opening, rarely played and well met by 2...c6 or 2...Nf6.
• 2.Ne2, Alapin's Opening, another offbeat try for White.
• 2.Ke2, the Bongcloud Attack, considered a joke opening.