user2061: I am new to chess and am confused on what to do with the following opening
[fen ""]

1. e4 e5
2. Nf3 Nf6
3. Nc3 Bb4

I have been playing 4. a3, but the Bishop then proceeds to take c3 so I end up with a doubled pawn.
If someone could offer some guidance or tell me what this opening is called so I can do some research, it would be very much appreciated.
Cheers

user1856: 4. a3 should be a good move. It's like a reverse Ruy Lopez with an extra tempo.
You can look it up in any opening database. Here's one (free): http://www.shredderchess.com/online-chess/online-databases/opening-database.html

user2042: I will be brief with the answer, ask for further clarifications/advices if you need them:
The opening is called Petroff's defense, but you have played a sideline in your game.
The ECO code of the opening is C42.
It usually goes like one of these two:

e4 e5
Nf3 Nf6

And now first line is: 3. Nxe5
Second one is : 3. d4
Your move is a sideline, I have never played it before, but you can look it up, it is not necessarily bad.
Hopefully this helps.
Good luck.
Best regards.

user2001: This opening is known as the Petrov three knights game. You can use this link to do a bit more research (http://www.365chess.com/eco/C42_Petrov_three_knights_game). I usually grab directly on e5 instead of protecting on e4. For example, here is a possible line:
[FEN ""]
1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 Nxc3 6.dxc3

White will follow up with Bc1-f4, Qd1-d2 and O-O-O. Then launch a pawn storm on the kingside (with the g and h pawns) in case black castles O-O. If black castles O-O-O, then the game will be a bit less sharp. Definitely worth a try!

user478: Edit: Using the chessgames Opening Explorer, I confirmed the move is playable, here is the list of possible replays:
Move     #games
---------------
4.Nxe5   175
4.Bc4    151
4.d3     52
4.a3     14
4.Nd5    12 <- my option
4.Be2    2
4.d4     2
4.Bd3    1
4.g3     1

4.Nd5 looks viable and easily prevents that double pawn.
It also pushes the game into an aggressive one, which can be good or bad depending on your play-style.
Final position after 4.Nd5:
rnbqk2r/pppp1ppp/5n2/3Np3/1b2P3/5N2/PPPP1PPP/R1BQKB1R b KQkq - 5 4

He will most likely do NxN, I don't see many other choices here as both the Bishop and the e Pawn are attacked:

4...Nxd5
4...Bd6 (weak move)
4...a5 (weak move)


2061: <p>I am new to chess and am confused on what to do with the following opening</p>

<pre><code>[fen ""]

1. e4 e5
2. Nf3 Nf6
3. Nc3 Bb4
</code></pre>

<p>I have been playing <code>4. a3</code>, but the Bishop then proceeds to take c3 so I end up with a doubled pawn.</p>

<p>If someone could offer some guidance or tell me what this opening is called so I can do some research, it would be very much appreciated.</p>

<p>Cheers</p>
 1856: <p><code>4. a3</code> should be a good move. It's like a reverse Ruy Lopez with an extra tempo.</p>

<p>You can look it up in any opening database. Here's one (free): <a href="http://www.shredderchess.com/online-chess/online-databases/opening-database.html" rel="nofollow">http://www.shredderchess.com/online-chess/online-databases/opening-database.html</a></p>
 2042: <p>I will be brief with the answer, ask for further clarifications/advices if you need them:</p>

<p>The opening is called <strong><em>Petroff's defense</em></strong>, but you have played a sideline in your game.</p>

<p>The <strong><em>ECO code</em></strong> of the opening is <strong><em>C42</em></strong>.</p>

<p>It usually goes like one of these two:</p>

<ol>
<li>e4 e5</li>
<li>Nf3 Nf6</li>
</ol>

<p>And now first line is: 3. Nxe5<br>
Second one is : 3. d4</p>

<p>Your move is a sideline, I have never played it before, but you can look it up, it is not necessarily bad.</p>

<p>Hopefully this helps.</p>

<p>Good luck.</p>

<p>Best regards.</p>
 2001: <p>This opening is known as the Petrov three knights game. You can use this link to do a bit more research (<a href="http://www.365chess.com/eco/C42_Petrov_three_knights_game" rel="nofollow">http://www.365chess.com/eco/C42_Petrov_three_knights_game</a>). I usually grab directly on e5 instead of protecting on e4. For example, here is a possible line:</p>

<pre><code>[FEN ""]
1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 Nxc3 6.dxc3
</code></pre>

<p>White will follow up with Bc1-f4, Qd1-d2 and O-O-O. Then launch a pawn storm on the kingside (with the g and h pawns) in case black castles O-O. If black castles O-O-O, then the game will be a bit less sharp. Definitely worth a try!</p>
 478: <p><strong>Edit:</strong> Using the <a href="http://www.chessgames.com/perl/explorer?node=1928652&amp;move=4&amp;moves=e4.e5.Nf3.Nf6.Nc3.Bb4&amp;nodes=21720.21721.21722.24467.24468.1928652" rel="nofollow">chessgames Opening Explorer</a>, I confirmed the move is playable, here is the list of possible replays:</p>

<pre><code>Move     #games
---------------
4.Nxe5   175
4.Bc4    151
4.d3     52
4.a3     14
4.Nd5    12 &lt;- my option
4.Be2    2
4.d4     2
4.Bd3    1
4.g3     1
</code></pre>

<p><strong>4.Nd5</strong> looks viable and easily prevents that double pawn.</p>

<p>It also pushes the game into an aggressive one, which can be good or bad depending on your play-style.</p>

<p>Final position after <strong>4.Nd5</strong>:</p>

<pre><code>rnbqk2r/pppp1ppp/5n2/3Np3/1b2P3/5N2/PPPP1PPP/R1BQKB1R b KQkq - 5 4
</code></pre>

<p>He will most likely do NxN, I don't see many other choices here as both the Bishop and the e Pawn are attacked:</p>

<ul>
<li>4...Nxd5</li>
<li>4...Bd6 (weak move)</li>
<li>4...a5 (weak move)</li>
</ul>
