user2466: I am not new to chess, I have been playing for around 6 years. But I don't know much about chess openings technically. What are some of the very good books to learn important opening moves?

user10810: Some chess opening books for beginners, I can recommend:

Chess Openings by Michael Basman
Discovering Chess Openings: Building Opening Skills from Basic Principles
By John Emms
Mastering the Chess Openings: Unlocking the Mysteries of the Modern Chess Openings, Volume 1 By John Watson


user3533: A classic reference book (or more like an encyclopedia) is Modern Chess Openings (or colloquially, MCO) by Nick de Firmian. While it doesn't have a lot of discussion on chess openings or the strategy behind a chess opening, and is noted for typos, it is extensive in types of commonly used openings. Definitely not easy reading. I believe the most recent edition is the 15th. Again, it will not teach you strategy behind the moves, but for that, I would pick up books specific to the opening you want to learn. Additionally, nothing can substitute good old fashioned tournament experience.

user3456: Mastering the Chess Openings in 4 Volumes by John Watson:
https://www.amazon.com/Mastering-Chess-Openings-Unlocking-Mysteries/dp/1904600603/ref=sr_1_sc_1?s=books&ie=UTF8&qid=1469395910&sr=1-1-spell&keywords=mastering+ches+openings+john+watson

user3357: Both Sam Collins and Paul van der Sterren's books I also highly recommend. Besides books youtube is also a great source for learning about openings. Both thechesswebsite and Dereque Kelly's channels are excellent for such.
For learning about specific openings I can recommend the Starting Out series by Everyman Chess which covers the selected opening in a very clear and instructive manner, also covering its variations.
For a more advanced look at an opening the Grandmaster Repertoire series by Quality Chess is top notch. Likewise any opening book published by Quality Chess is of good quality. http://www.qualitychess.co.uk
Of course Everyman Chess also produces more advanced openings books such as the Play the... (or Play...) and Move by Move series. http://www.everymanchess.com
The Chess Opening Essentials series by New In Chess is great, the series of four books covers various openings from the various defenses to 1.e4 to 1.d4 and so forth. http://www.newinchess.com/Chess_Opening_Essentials__Vol__1___4-p-1930.html
Winning Chess Openings by Yasser Seirawan is fantastic http://www.amazon.com/Winning-Chess-Openings-Everyman/dp/1857443497/ref=sr_1_8?s=books&ie=UTF8&qid=1406887013&sr=1-8&keywords=Chess+openings
I assume at your level it is much more beneficial to know about the basic ideas of an opening rather than memorizing lines which stem from it. A simple google search can inform you greatly about an opening. If there is any opening book you should buy let it be one which covers many openings and presents the various ideas behind them. The already mentioned books are all excellent and I would like to add to their recommendation. I can only offer by this post some more fantastic books and advanced ones for if you progress to that level.

user-1: Irving Chernev's Logical Chess annotates 33 games in a really accessible way, including the openings.
Each move gets a detailed explanation of its pros & cons in an accessible way (i.e. more engaging text, less variations), e.g. explaining how to exploit a lead in development or control of the centre.
The openings that feature the most are:

Queen's gambit declined (there is a whole chapter dedicated to queen's pawn openings)
Nimzo-Indian defence, mainline
The Italian Game
The Ruy Lopez

But there are a few others as well (I'm guessing from your question that you're not after any specific opening)
The chapters cover:

Attacking the King
Queen's pawn opening
Master games, with an emphasis of those played by Capablanca

Also, you asked for books but the YouTube videos by National Master Dereque Kelley where he runs through the mainlines of many common openings are very good to!

user2489: You'll hear many masters tell any chess enthusiast of the "beginner" to intermediate level to pick of the books "Winning chess strategies for kids" by Jeff Coakley (which doesn't read like a kids book and is fantastically written) and "Chess strategies for club members" by Herman Grooten.
Also, chess.com has a great opening explorer. There's always YouTube as well! Hope that helps.

user863: The Complete Book of Chess Strategy by Silman. Just saw this yesterday for the first time and its the first Chess Book I felt I had to spend the money on. Simple, easy to digest and full of tactics and strategy. I'm already finding myself playing better in just one day as a direct result. I find a lot of the above books to either be to loaded with notation and grand master games to be useful to a beginner, or in the case of Collins' Understanding Chess Openings, to be a bit over the top in his language.
Compare if you will:

The development of White's bishop to c4 prepares castling, eyes the f7-pawn and hinders an early ...d5. We would need a pretty compelling reason not to play such an obviously logical move and unfortunately such abstention is justified by the fact that Black, by most accounts, has a pretty easy route to equality in all variations. Attention has thus moved away from the Italian Game, with its more durable neighbour the Spanish Game (Ruy Lopez) proving a more promising route to an enduring edge for White.

-Collins
There's just much easier ways to say the same ideas. All he does is make it more confusing.
Compare that with some text from Silman:

While the Caro-Kann (1.e4 c6 2.d4 d5) and the French Defense (1.e4 e6 2.d4 d5) both strive to gain a central foothold with a defended d5-pawn, the Caro leads to calmer positions than its French brother. On the positive side, the move ...c6(instead of ...e6) keeps the c8-h3 diagonal open for Black's light-squared Bishop. The negative side of this opening revolves around the fact that ...c7-c5 is still an important source of counterplay and, as compared to the French, Black has already moved this pawn and lost a tempo as a result. This slight loss of time in playing ...c7-c6 followed by a later ...c6-c5 means that Black will try to slow the play down.

-Silman
Silman's book is just great in my opinion for beginners because of how clear and easy to use it is.

user1485: It depends on what you are after and what your level is, but John Watson's Mastering the Chess Openings series has a good reputation.

user2399: If you're not familiar with openings your best bet would be to start with a decent general book on openings rather than going for something too specific. Being familiar with chess you will probably have settled on what kind of player you are, and therefore what types of openings suit your style. 
Your first task should be to find the kinds of openings that suit you by studying something broad. Once you've found the types of openings you like you can then focus on learning more specific openings with more specific books. 
Sorry I don't know any books off the top of my head. I prefer to learn openings by playing and supplementing this with general internet searches.

user2115: I like "Chess Opening for Dummies". It features the main openings with two commented games for each one: one game in which white wins and one in which black wins. This allows to avoid bias toward the choice of adding an opening in the repertoire.

user291: There are two excellent modern surveys of openings: Sam Collins' Understanding the Chess Openings and Paul van der Sterren's Fundamental Chess Openings. They both cover every major opening, demonstrating the main ideas and variations. I would start with Collins, since it is shorter and easier to read through in its entirety, but both are highly recommended.

2466: <p>I am not new to chess, I have been playing for around 6 years. But I don't know much about chess openings technically. What are some of the very good books to learn important opening moves?</p>
 10810: <p>Some chess opening books for beginners, I can recommend:</p>

<ul>
<li>Chess Openings by Michael Basman</li>
<li>Discovering Chess Openings: Building Opening Skills from Basic Principles
By John Emms</li>
<li>Mastering the Chess Openings: Unlocking the Mysteries of the Modern Chess Openings, Volume 1 By John Watson</li>
</ul>
 3533: <p>A classic reference book (or more like an encyclopedia) is Modern Chess Openings (or colloquially, MCO) by Nick de Firmian. While it doesn't have a lot of discussion on chess openings or the strategy behind a chess opening, and is noted for typos, it is extensive in types of commonly used openings. Definitely not easy reading. I believe the most recent edition is the 15th. Again, it will not teach you strategy behind the moves, but for that, I would pick up books specific to the opening you want to learn. Additionally, nothing can substitute good old fashioned tournament experience.</p>
 3456: <p>Mastering the Chess Openings in 4 Volumes by John Watson:</p>

<p><a href="http://rads.stackoverflow.com/amzn/click/1904600603" rel="nofollow">https://www.amazon.com/Mastering-Chess-Openings-Unlocking-Mysteries/dp/1904600603/ref=sr_1_sc_1?s=books&amp;ie=UTF8&amp;qid=1469395910&amp;sr=1-1-spell&amp;keywords=mastering+ches+openings+john+watson</a></p>
 3357: <p>Both Sam Collins and Paul van der Sterren's books I also highly recommend. Besides books youtube is also a great source for learning about openings. Both thechesswebsite and Dereque Kelly's channels are excellent for such.</p>

<p>For learning about specific openings I can recommend the Starting Out series by Everyman Chess which covers the selected opening in a very clear and instructive manner, also covering its variations.</p>

<p>For a more advanced look at an opening the Grandmaster Repertoire series by Quality Chess is top notch. Likewise any opening book published by Quality Chess is of good quality. <a href="http://www.qualitychess.co.uk" rel="nofollow">http://www.qualitychess.co.uk</a></p>

<p>Of course Everyman Chess also produces more advanced openings books such as the Play the... (or Play...) and Move by Move series. <a href="http://www.everymanchess.com" rel="nofollow">http://www.everymanchess.com</a></p>

<p>The Chess Opening Essentials series by New In Chess is great, the series of four books covers various openings from the various defenses to 1.e4 to 1.d4 and so forth. <a href="http://www.newinchess.com/Chess_Opening_Essentials__Vol__1___4-p-1930.html" rel="nofollow">http://www.newinchess.com/Chess_Opening_Essentials__Vol__1___4-p-1930.html</a></p>

<p>Winning Chess Openings by Yasser Seirawan is fantastic <a href="http://rads.stackoverflow.com/amzn/click/1857443497" rel="nofollow">http://www.amazon.com/Winning-Chess-Openings-Everyman/dp/1857443497/ref=sr_1_8?s=books&amp;ie=UTF8&amp;qid=1406887013&amp;sr=1-8&amp;keywords=Chess+openings</a></p>

<p>I assume at your level it is much more beneficial to know about the basic ideas of an opening rather than memorizing lines which stem from it. A simple google search can inform you greatly about an opening. If there is any opening book you should buy let it be one which covers many openings and presents the various ideas behind them. The already mentioned books are all excellent and I would like to add to their recommendation. I can only offer by this post some more fantastic books and advanced ones for if you progress to that level.</p>
 -1: <p>Irving Chernev's <em>Logical Chess</em> annotates 33 games in a really accessible way, including the openings.</p>

<p>Each move gets a detailed explanation of its pros &amp; cons in an accessible way (i.e. more engaging text, less variations), e.g. explaining how to exploit a lead in development or control of the centre.</p>

<p>The openings that feature the <em>most</em> are:</p>

<ul>
<li>Queen's gambit declined (there is a whole chapter dedicated to queen's pawn openings)</li>
<li>Nimzo-Indian defence, mainline</li>
<li>The Italian Game</li>
<li>The Ruy Lopez</li>
</ul>

<p>But there are a few others as well (I'm guessing from your question that you're not after any specific opening)</p>

<p>The chapters cover:</p>

<ul>
<li><p>Attacking the King</p></li>
<li><p>Queen's pawn opening</p></li>
<li><p>Master games, with an emphasis of those played by Capablanca</p></li>
</ul>

<p>Also, you asked for books but the YouTube videos by National Master Dereque Kelley where he runs through the mainlines of many common openings are very good to!</p>
 2489: <p>You'll hear many masters tell any chess enthusiast of the "beginner" to intermediate level to pick of the books "Winning chess strategies for kids" by Jeff Coakley (which doesn't read like a kids book and is fantastically written) and "Chess strategies for club members" by Herman Grooten.</p>

<p>Also, chess.com has a great opening explorer. There's always YouTube as well! Hope that helps.</p>
 863: <p><a href="http://rads.stackoverflow.com/amzn/click/1890085014" rel="nofollow">The Complete Book of Chess Strategy</a> by Silman. Just saw this yesterday for the first time and its the first Chess Book I felt I had to spend the money on. Simple, easy to digest and full of tactics and strategy. I'm already finding myself playing better in just one day as a direct result. I find a lot of the above books to either be to loaded with notation and grand master games to be useful to a beginner, or in the case of Collins' <em>Understanding Chess Openings</em>, to be a bit over the top in his language.</p>

<p>Compare if you will:</p>

<blockquote>
  <p>The development of White's bishop to c4 prepares castling, eyes the f7-pawn and hinders an early ...d5. We would need a pretty compelling reason not to play such an obviously logical move and unfortunately such abstention is justified by the fact that Black, by most accounts, has a pretty easy route to equality in all variations. Attention has thus moved away from the Italian Game, with its more durable neighbour the Spanish Game (Ruy Lopez) proving a more promising route to an enduring edge for White.</p>
</blockquote>

<p><em>-Collins</em></p>

<p>There's just much easier ways to say the same ideas. All he does is make it more confusing.</p>

<p>Compare that with some text from Silman:</p>

<blockquote>
  <p>While the Caro-Kann (1.e4 c6 2.d4 d5) and the French Defense (1.e4 e6 2.d4 d5) both strive to gain a central foothold with a defended d5-pawn, the Caro leads to calmer positions than its French brother. On the positive side, the move ...c6(instead of ...e6) keeps the c8-h3 diagonal open for Black's light-squared Bishop. The negative side of this opening revolves around the fact that ...c7-c5 is still an important source of counterplay and, as compared to the French, Black has already moved this pawn and lost a tempo as a result. This slight loss of time in playing ...c7-c6 followed by a later ...c6-c5 means that Black will try to slow the play down.</p>
</blockquote>

<p><em>-Silman</em></p>

<p>Silman's book is just great in my opinion for beginners because of how clear and easy to use it is.</p>
 1485: <p>It depends on what you are after and what your level is, but John Watson's <a href="http://www.gambitbooks.com/books/Mastering_the_Chess_Openings_volume_1.html" rel="noreferrer">Mastering the Chess Openings</a> series has a good reputation.</p>
 2399: <p>If you're not familiar with openings your best bet would be to start with a decent general book on openings rather than going for something too specific. Being familiar with chess you will probably have settled on what kind of player you are, and therefore what types of openings suit your style. </p>

<p>Your first task should be to find the kinds of openings that suit you by studying something broad. Once you've found the types of openings you like you can then focus on learning more specific openings with more specific books. </p>

<p>Sorry I don't know any books off the top of my head. I prefer to learn openings by playing and supplementing this with general internet searches.</p>
 2115: <p>I like "Chess Opening for Dummies". It features the main openings with two commented games for each one: one game in which white wins and one in which black wins. This allows to avoid bias toward the choice of adding an opening in the repertoire.</p>
 291: <p>There are two excellent modern surveys of openings: Sam Collins' <em>Understanding the Chess Openings</em> and Paul van der Sterren's <em>Fundamental Chess Openings</em>. They both cover every major opening, demonstrating the main ideas and variations. I would start with Collins, since it is shorter and easier to read through in its entirety, but both are highly recommended.</p>
