The Greco Defence (or McConnell Defence), named after Gioachino Greco (c. 1600 – c. 1634), is a chess opening that begins with the moves: The opening is categorised by Encyclopaedia of Chess Openings as code C40.

Of the several plausible ways Black has to defend his e-pawn, 2...Qf6 is considered one of the weaker choices, since the queen is developed prematurely and can become a target for attack.

Also, the black knight on g8 is deprived of its most natural square.

There is, however, no obvious refutation of this opening; White's advantage consists mainly of smoother development.

Although it is a popular opening choice by novice players, it has also been used by players who, according to International Master Gary Lane, "should know better".

Greco himself illustrated the following amusing line against this defence in 1620: 1. e4 e5 2.