2.Nf3
The most popular second move for White is 2.Nf3 (the King's Knight Opening), attacking Black's king pawn, preparing to castle kingside , and preparing for d2–d4.
2...Nc6
Black's most common reply to 2.Nf3 is 2...Nc6. This can lead to the Ruy Lopez (3.Bb5), one of the most popular openings at all levels of chess, and one of the most extensively analyzed.
The Italian Game (3.Bc4) is a popular alternative, usually leading to either the Giuoco Piano (3...Bc5) or the Two Knights Defense (3...Nf6).
The Scotch Game (3.d4) was popular in the 19th century and remains so at amateur level. After 3...exd4 White may either recapture with 4.Nxd4, usually leading to an equal game, or play the Scotch Gambit (4.Bc4), a dangerous tactical line against an unprepared opponent.
3.Nc3 Nf6, the Four Knights Game, was often played in the late 19th to early 20th century. Less commonly, 3....g6 or ...Bb4, (the Three Knights Game), are possible.
The Ponziani Opening (3.c3) 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.
Other second moves for Black
Black's most popular alternative to 2...Nc6 is 2...Nf6, usually leading to Petrov's Defense, though White can avoid the extensive theory of the Petrov by playing 3.Nc3.
The Philidor Defense (2...d6) 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; however, it is still occasionally seen at grandmaster level.
The Gunderam Defense (2...Qe7) is an offbeat choice which blocks the development of the king's bishop, and has never achieved widespread popularity.
The Elephant Gambit (2...d5) and the Latvian Gambit (2...f5) are considered very risky for Black, with the latter usually seen only in correspondence play. The Damiano Defense (2...f6) may be met by either 3.Nxe5 or 3.Bc4 with advantage and is almost never seen.
Other second moves for White
The most popular alternatives to 2.Nf3 are 2.f4 (the King's Gambit), 2.Nc3 (the Vienna Game), and 2.Bc4 (the Bishop's Opening). These three openings have some similarities; some of the quieter lines in the Vienna and Bishop's Opening can transpose to positional variations of the King's Gambit Declined, when White plays f2–f4 before playing Nf3. The King's Gambit was popular in the nineteenth century with grandmaster and amateur alike. White offers a pawn for speedy development, as well as to attack Black's central outpost. The Vienna Game also frequently features attacks on the Black center by means of f2–f4.
In the Center Game (2.d4), White immediately opens the center, though if the pawn is to be recovered after 2...exd4, White must prematurely develop their queen. An alternative is to sacrifice one or two pawns by offering the Danish Gambit (3.c3).
The early development of the queen in the Danvers Opening, also known as the Parham Attack (2.Qh5), is usually played only by amateurs, though Hikaru Nakamura has experimented with it in grandmaster tournaments and was able to achieve a reasonable position. [2] [3] The Napoleon Opening, 2.Qf3, has even less to recommend it as Black can easily block any mating threats without compromising their development. The Portuguese Opening (2.Bb5) and Alapin's Opening (2.Ne2) are offbeat tries for White, but neither gain any advantage against correct play. The Bongcloud Attack (2.Ke2) is considered a joke opening.
