The Ponziani Opening is a chess opening that begins with the moves:

It is one of the oldest chess openings, having been discussed in literature by 1497. It was advocated by Howard Staunton, generally considered the world's strongest player from 1843 to 1851, in his 1847 book The Chess-Player's Handbook. For some decades, it was often called "Staunton's Opening" or the "English Knight's Game" as a result. Today, it is usually known by the name of Domenico Lorenzo Ponziani, whose main contribution to the opening was his introduction of the countergambit 3...f5!? in 1769.

Although it is considered inferior to other third move options such as the Ruy Lopez (3.Bb5), it has a reputation for leading to sharp and dynamic play. It is typically only used as a surprise weapon by modern players. The move c3 supports a later d4 push and also enables early development of the queen, with White frequently playing Qa4. Black's usual response is either 3...Nf6 or 3...d5. Magnus Carlsen used it for a victory in 2013. Ponziani's countergambit 3...f5!? was successfully played in a grandmaster game between Hikaru Nakamura and Julio Becerra Rivero at the US Championship 2007.

The Ponziani is one of the oldest known openings, having been first discussed in chess literature by no later than 1497. It was mentioned in both of the earliest chess treatises: the Repetición de Amores y Arte de Ajedrez con ci Iuegos de Partido by Lucena and the Göttingen manuscript. Today the opening bears the surname of Domenico Lorenzo Ponziani. Although Ponziani did analyze the opening in 1769, his principal contribution was the introduction of the countergambit 3...f5!? Later the opening was favored by Howard Staunton, who in The Chess-Player's Handbook (1847) called it "so full of interest and variety, that its omission in many of the leading works on the game is truly unaccountable. ... it deserves, and, if we mistake not, will yet attain a higher place in the category of legitimate openings than has hitherto been assigned to it."

Staunton cumbersomely referred to the opening as "The Queen's Bishop's Pawn Game in the King's Knight's Opening", as did George H. D. Gossip in The Chess Player's Manual (1888, American edition 1902). Napoleon Marache, one of the leading American players, similarly called it the "Queen's Bishop's Pawn Game" in his 1866 manual. In their treatise Chess Openings Ancient and Modern (1889, 1896), E. Freeborough and the Reverend C.E. Ranken called it "Staunton's Opening". In an appendix to later editions of Staunton's work, R.F. Green, editor of British Chess Magazine, also called it "Staunton's Opening", directing those seeking a definition of "Ponziani's Game" to the former name. Green referred to 3...f5 as "Ponziani's Counter Gambit". Chess historian H. J. R. Murray in his celebrated 1913 work A History of Chess called the opening simply the "Staunton", explaining that he was using "the ordinary names of the Openings as used by English players of the present day". James Mason in his treatise The Art of Chess (Fourth Edition c. 1910?) referred to the opening as the "Ponziani–Staunton Attack". The famous German Handbuch des Schachspiels, which went through eight editions between 1843 and 1916, called it the "Englisches Springerspiel" (English Knight's Game). The Reverend E.E. Cunnington in The Modern Chess Primer (Thirteenth Edition 1933) referred to it as the "Ponziani Opening (sometimes called Staunton's)".

Wilhelm Steinitz, the first World Champion, in his 1895 treatise The Modern Chess Instructor (Part II), called the opening the "Ponziani Opening", as did his successor, Emanuel Lasker, in Lasker's Manual of Chess. Similarly, Frank Marshall in Chess Openings, the authors of Modern Chess Openings (Second Edition 1913), and Siegbert Tarrasch in The Game of Chess (1931, English translation 1938) called it "Ponziani's Opening". William Cook in The Chess Players' Compendium (Fifth Edition 1910) called it "Ponziani's Game", while Francis Joseph Lee and Gossip in The Complete Chess – Guide (1903) called it "Ponziani's Knight's Game". Contemporary authors likewise call it the "Ponziani Opening", "Ponziani's Opening", or simply the "Ponziani".

The Ponziani is rarely played today except as a surprise weapon, because Black has the pleasant choice between equalizing easily and attempting to obtain an advantage with sharper play. White's third move prepares to build a powerful pawn center with 4.d4, a logical objective also seen in the more popular Ruy Lopez and Giuoco Piano. However, 3.c3 is somewhat premature because the move: 1) takes away the most natural square for White's queen knight, 2) temporarily creates a hole on d3, and 3) develops a pawn rather than a piece, leaving White behind in development and not well placed to meet a counterattack in the center. Moreover, unlike in the Giuoco Piano, where White's d4 advance attacks Black's king bishop on c5, in the Ponziani d4 will not gain a tempo. On the positive side, the move 3.c3 creates a second diagonal for the white queen.

As early as 1904, Marshall wrote that, "There is no point in White's third move unless Black plays badly. ... White practically surrenders the privilege of the first move." More recently, Graham Burgess called the Ponziani "a relic from a bygone age, popular neither at top level nor at club level". Bruce Pandolfini has said,