The Cubists by Paul Waldo Schwartz (Thames & Hudson 1971)

This book is part of the Thames & Hudson History of Art Series and is really well written and constructed, every painting that is pictured is carefully referred to in the text with easy marginal notes making navigation very easy.  The text is well written if a little heavy going, and my only complaint would be that more of the images were not in colour which was of such fundamental importance for the works of the Cubists, but then you can now look them up online.