ECO D66

ECO D00–D99 — Closed and Semi-Closed Games: 1.d4 d5 queen's pawn openings and the Grünfeld Defense.

2 named opening lines are classified under ECO code D66.

• Queen's Gambit Declined: Orthodox Defense, Bd3 Line — 1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Bg5 Be7 5.e3 O-O 6.Nf3 Nbd7 7.Rc1 c6 8.Bd3
• Queen's Gambit Declined: Orthodox Defense, Fianchetto Variation — 1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Bg5 c6 5.Nf3 Be7 6.e3 Nbd7 7.Rc1 O-O 8.Bd3 dxc4 9.Bxc4 b5