The Scandinavian Defense begins with d5 against e4. Black challenges the center immediately, rather than preparing the break with ... c5 or ... e5 as in most other replies to e4.
1. e4 d5 2. exd5 ♛xd5
White almost always recaptures with 2. exd5. The two remaining tries, 2. e5 and 2. ♘c3, give Black an easy game; the first transposes to a favorable French-like structure, and the second allows 2... dxe4.
After the natural capture 2... ♛xd5, White gains a tempo with 3. ♘c3, and the queen has to move again. This tempo is the price Black pays for meeting the center immediately, and everything the various lines revolves around how Black spends it.
1. e4 d5 2. exd5 ♛xd5 3. ♘c3
Black has three retreats: ... ♛a5, the most popular; ... ♛d6, more central; and ... ♛d8, the most modest. Any other square is worse, because White develops with an extra tempo and a lead in the center.
The queen goes to a5, staying on the active a5-e1 diagonal, where it eyes the e1-square and, later, the d2-bishop.
1. e4 d5 2. exd5 ♛xd5 3. ♘c3 ♛a5 4. d4 ♞f6 5. ♘f3 c6 6. ♗c4 ♝f5 7. ♗d2 e6
This is the main position of the opening, reachable by several move orders. Black's structure, pawns on c6 and e6 with the bishop developed on f5 before ... e6, closely resembles the Caro-Kann, which is why many Caro-Kann players adopt this line. A feature of the position is that either side can castle on either side, so the resulting middlegame can take different shapes.
The move ... c6 should not be delayed. It gives the queen the c7-square, so that ♗d2 no longer gains a tempo by attacking it. Playing ... e6 and castling too early, before ... c6, can allow White's pieces to chase the queen.
From here White has two main tries:
Black's plan is the same against both: complete development with ... ♝b4 or ... ♝e7, ... O-O or ... O-O-O depending on White's choice, and look for the freeing break ... c5.
Two other move-order points are worth knowing:
A sharper try is the pawn sacrifice on move four:
1. e4 d5 2. exd5 ♛xd5 3. ♘c3 ♛a5 4. b4
If Black takes the pawn, White gets play against the queen. With correct defense, however, Black should be able to hold the extra material without much risk. A way to sidestep the tries is to delay the gambit by one move with 4. ♘f3 ♞f6 5. b4 ♛xb4 6. a4, intending ♗c1-a3 to develop with tempo against the queen.
The queen can also stay more central, on d6. For a long time this move was considered dubious, because the queen looks exposed to ♘b5 and ♗f4, but modern practice has shown it to be playable.
1. e4 d5 2. exd5 ♛xd5 3. ♘c3 ♛d6 4. d4 ♞f6 5. ♘f3 a6
The move ... a6 is a typical precaution, taking the b5-square away from White's knight. White's effective setup against this queen placement is d4, ♘f3, g3, ♗g2, and O-O, followed by ♘e5 at some moment, aiming for an active central position rather than chasing the queen directly.
Black should keep the queen's move with the plan is ... c6 or ... g6, ordinary development, and only then a central break. There is a possible tempo-gaining ♗f4 or ♘b5, for example after 5... c6?! 6. ♗f4 ♛b4, when the queen is pushed to an awkward square.
The most modest retreat returns the queen back to the home square.
1. e4 d5 2. exd5 ♛xd5 3. ♘c3 ♛d8 4. d4 ♞f6 5. ♘f3 ♝g4
Black loses more time than in the other two retreats, but keeps no weaknesses at all, and the resulting game is a solid, Caro-Kann-like structure with an extra tempo for White.
One older try, 4... g6, intending a fianchetto with ... ♞h6, has a poor reputation so the development with 4... ♞f6 is the safer choice.
The remaining queen moves on move three are considered inferior, and it is worth knowing why, since they occasionally appear from unprepared opponents.
1. e4 d5 2. exd5 ♛xd5 3. ♘c3 ♛e5+ 4. ♗e2 c6 5. ♘f3 ♛c7 6. d4
After 3... ♛e5+, White develops with tempo and obtains a comfortable lead in development. The queen has visited three different squares by move six.
1. e4 d5 2. exd5 ♛xd5 3. ♘c3 ♛e6+ 4. ♗e2 ♛g6 5. ♘f3 ♛xg2 6. ♖g1 ♛h3 7. d4
This line is a trap: Black wins the g2-pawn, but White obtain a great lead in development.
Instead of recapturing with the queen at once, Black can play 2... ♞f6, delaying the recapture and taking on d5 with the knight instead. This avoids the tempo loss of the queen lines, at the cost of a slightly less active setup.
1. e4 d5 2. exd5 ♞f6 3. d4 ♞xd5
The move 3. d4 is White's most popular choice, allowing Black to regain the pawn while White focuses on quick development. After 3... ♞xd5, White commonly continues 4. c4, forcing the knight to move again, and Black has three tries: ... ♞b6, the most active; ... ♞f6, a sound retreat; and ... ♞b4.
1. e4 d5 2. exd5 ♞f6 3. d4 ♞xd5 4. c4 ♞b6 5. ♘c3 g6
Black often fianchettoes the bishop and completes development quickly, aiming to pressure White's center from the flank. Because the queen never leaves its original square, White's tempo-gaining moves from the ... ♛xd5 lines are absent, and the game takes on more of an ordinary open-game character.
Two other move orders deserve a mention. After 3. ♘f3, the game tends to transpose into other lines. After 3. ♗b5+, a common continuation is 3... ♝d7 4. ♗c4 ♞xd5, and White's bishop on c4 can become a target for ... b5 ideas later on.
Two gambits are built on the same idea after 2... ♞f6: Black delays the recapture even further, offering a pawn for rapid development. They are separate bodies of theory, and both are considered unsound with correct defense, but they are surprise weapons that catch unprepared opponents.
The Portuguese Variation delays the recapture with a piece move:
1. e4 d5 2. exd5 ♞f6 3. d4 ♝g4 4. f3 ♝f5 5. ♗b5+ ♞bd7 6. c4
Black leaves the pawn on d5 uncaptured for several moves in exchange for fast piece activity, and the position is sharp and imbalanced.
The Icelandic Gambit, follows the same idea but opens the center with a pawn break instead:
1. e4 d5 2. exd5 ♞f6 3. c4 e6 4. dxe6 ♝xe6
Black regains one of the pawns immediately and obtains open lines for both bishops and a lead in development, in exchange for the other pawn still missing.
Both gambits require detailed preparation, and should be treated them as separate openings to study later rather than as part of the main repertoire covered here.