Fundamental Chess Openings.
Books on openings
http://www.thechessmind.net/blog/2010/1/30/a-brief-review-of-carsten-hansens-back-to-basics-openings.html
https://web.archive.org/web/20140627031504/http://www.chesscafe.com/text/hansen76.pdf
http://www.gambitbooks.com/pdfs/Understanding_the_Chess_Openings.pdf
https://web.archive.org/web/20140626173432/http://www.chesscafe.com/text/hansen128.pdf
http://www.gambitbooks.com/pdfs/FCO_Fundamental_Chess_Openings.pdf

The "Chess For Dummies" book isn't bad for a quick survey of the openings.
Nor is wiki for the major openings.
For something in between a survey and the various encyclopedias, John Watson's 3-vol "Mastering the Chess Openings" is pretty amazing.

The "Chess For Dummies" book isn't bad for a quick survey of the openings.
Nor is wiki for the major openings.
For something in between a survey and the various encyclopedias, John Watson's 3-vol "Mastering the Chess Openings" is pretty amazing.
Watson's series is 4 books, not 3.
Book 1 - 1.e4
Book 2 - 1.d4
Book 3 - 1.c4
Book 4 - All Others
https://web.archive.org/web/20140627115737/http://www.chesscafe.com/text/hansen99.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_1.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_2.pdf
https://web.archive.org/web/20140626220240/http://www.chesscafe.com/text/hansen117.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_3.pdf
https://web.archive.org/web/20140627070808/http://www.chesscafe.com/text/hansen137.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_4.pdf
I think this is a key sentence from the Watson introduction (apparently written at a time when the project was seen as consisting of only two volumes):
"As I began work on this book it became obvious that even in two large volumes it wouldn't be possible to cover every opening, nor even the most significant variations of every opening, and still achieve the insights that I hoped to convey."
As an example of a consequence of this: "I won't be dealing with the [1 e4 c6 2 d4 d5] 3 Nc3 main lines [in the Caro-Kann Defence], although naturally they're full of wonderful ideas."
1 e4 c6 2 d4 d5 3 Nc3 got about half of the space in the 14 page Caro-Kann chapter in FCO. Despite the ultimate size of his project, Watson, as far as I can tell, was not attempting to write a general reference work. His goal was to convey various insights. To judge the value of those insights for you, I would suggest a detailed examination of the reviews and book samples. The Watson series concludes with a discussion of various issues in connection with openings. I often refer to a quote from one passage:
"... For players with very limited experience, I recommend using openings in which the play can be clarified at an early stage, often with a degree of simplification. To accomplish this safely will take a little study, because you will have to get used to playing wiith open lines for both sides' pieces, but you can't eliminate risk entirely in the opening anyway. ... teachers all over the world suggest that inexperienced players begin with 1 e4. ... You will undoubtedly see the reply 1 ... e5 most often when playing at or near a beginner's level, ... After 2 Nf3, 2 ... Nc6 will occur in the bulk of your games. ... I recommend taking up the classical and instructive move 3 Bc4 at an early stage. Then, against 3 ... Bc5, it's thematic to try to establish the ideal centre by 4 c3 and 5 d4; after that, things can get complicated enough that you need to take a look at some theory and learn the basics; ... Of course, you can also play 1 d4 ... A solid and more-or-less universal set-up is 2 Nf3 and 3 Bf4, followed in most cases by 4 e3, 5 Be2 and 6 0-0. I'd rather see my students fight their way through open positions instead; however, if you're not getting out of the opening alive after 1 e4, this method of playing 1 d4 deserves consideration. ... a commonly suggested 'easy' repertoire for White with 1 Nf3 and the King's indian Attack ... doesn't lead to an open game or one with a clear plan for White. Furthermore, it encourages mechanical play. Similarly, teachers sometimes recommend the Colle System ..., which can also be played too automatically, and usually doesn't lead to an open position. For true beginners, the King's Indian Attack and Colle System have the benefit of offering a safe position that nearly guarantees passage to some kind of playable middlegame; they may be a reasonable alternative if other openings are too intimidating. But having gained even a small amount of experience, you really should switch to more open and less automatic play." - IM John Watson in a section of his 2010 book, Mastering the Chess Openings, Volume 4
I have my doubts about the degree to which books of this sort are helpful. FM Carsten Hansen wrote that Understanding the Chess Openings will "help you determine whether you would like to play certain openings", but I wonder if that can be effectively done without sample games. Comprehensive books often do not have room for sample games.

Good Chess Openings Books for Beginners and Beyond....some are broad & general, others are focused on specific openings....
https://www.chess.com/forum/view/chess-equipment/good-chess-opening-books-for-beginners-and-beyond
The best book for learning fundamental openings principles for the beginner-novice is...
"Discovering Chess Openings..." by John Emms....
The two best general openings references are....
"FCO: Fundamental Chess Openings" by Paul van der Sterren (a single volume)
and
"Mastering the Chess Openings..." by John Watson (4 volumes)

I have my doubts about the degree to which books of this sort are helpful. FM Carsten Hansen wrote that Understanding the Chess Openings will "help you determine whether you would like to play certain openings", but I wonder if that can be effectively done without sample games. Comprehensive books often do not have room for sample games.
The complete games format works well for books focused on specific openings. For general openings references however, such as the van der Sterren and John Watson books, inclusion of (annotated) sample games is generally not feasible due primarily to space and size related issues.
I agree that comprehensive openings books are not likely to have room for sample games. Nevertheless, I think that this limits their usefulness for the purpose identified by FM Carsten Hansen - helping one to determine what openings one would like to play. There is still the possibility of trying to read entirely through such a book, but I think that it is well to warn people about the difficulty to be encountered in getting much opening-selection help from such a project. There are available alternative resources to help one make choices. For some purposes, Fundamental Chess Openings is indeed a good choice, but, for opening-selection assistance, my guess is that one is better off with a shorter work. Mastering the Chess Openings does include a fair number of annotated games and is, as far as I can tell, a commendable work in other respects. Nevertheless, in view of the substantial cost, I think that potential buyers should be warned that it is not a reference in the usual sense. As IM John Watson himself indicated, coverage of some significant variations was sacrificed for the sake of providing insights.
MCO 15th Edition
Even back in 2008, FM Carsten Hansen felt it appropriate to write, "it pretends to be up-to-date and relevant in all chapters, but it isn’t".
https://web.archive.org/web/20140626165820/http://www.chesscafe.com/text/hansen110.pdf

I agree that comprehensive openings books are not likely to have room for sample games. Nevertheless, I think that this limits their usefulness for the purpose identified by FM Carsten Hansen - helping one to determine what openings one would like to play. There is still the possibility of trying to read entirely through such a book, but I think that it is well to warn people about the difficulty to be encountered in getting much opening-selection help from such a project. There are available alternative resources to help one make choices. For some purposes, Fundamental Chess Openings is indeed a good choice, but, for opening-selection assistance, my guess is that one is better off with a shorter work. Mastering the Chess Openings does include a fair number of annotated games and is, as far as I can tell, a commendable work in other respects. Nevertheless, in view of the substantial cost, I think that potential buyers should be warned that it is not a reference in the usual sense. As IM John Watson himself indicated, coverage of some significant variations was sacrificed for the sake of providing insights.
Spongey - I have no strong disagreement with your comments, which for the most part are certainly valid perspectives.
I agree that opening books which feature the complete games format are to be preferred. Also I acknowledge that John Watson's "Mastering the Chess Openings..." series also includes complete games in their coverage, which I had forgotten about. Watson's series, as well as the van der Sterren book, both of which I refer to as "references", are of a kind which are essentially devoted to broad coverage of most or all of the standard openings. In this regard they are to be distinguished from books devoted to a specific, single opening.
I agree that Mastering the Chess Openings should not be confused with books devoted to a specific, single opening, but, in view of the title, such a confusion seems unlikely to occur in any case. On the other hand, I don't think the title gives the potential buyer much of a clue that coverage of some significant variations was sacrificed for the sake of providing insights, and, indeed, the overall size of the project might cause the unwary buyer to believe otherwise.

I agree that Mastering the Chess Openings should not be confused with books devoted to a specific, single opening, but, in view of the title, such a confusion seems unlikely to occur in any case. On the other hand, I don't think the title gives the potential buyer much of a clue that coverage of some significant variations was sacrificed for the sake of providing insights, and, indeed, the overall size of the project might cause the unwary buyer to believe otherwise.
In a nutshell my response is....
If somehow I were to be allowed only 4 opening books for the rest of my chess career, I would have to choose John Watson's "Mastering the Chess Openings" series....
I choose to be concerned about the possibility of a potential buyer getting the wrong idea about the nature of a product.

I choose to be concerned about the possibility of a potential buyer getting the wrong idea about the nature of a product.
I think that most buyers would typically recognize that an openings "reference" which attempts to treat most if not all of the major openings would generally not provide the detailed depth of coverage of variations and latest theory that a book devoted to single opening could offer....
What's a good general book on openings? Something which you thought was well written and comprehensive. If it were quite broadly applicable that would be great, but it'd be nice to hear about some interesting books that people might have read...