The books *Classical Banach Spaces III* and *Classical Banach Spaces IV* by Joram Lindenstrauss and Lior Tzafriri never appeared (after having been promised in various places of volumes I and II). 

As written by Albrecht Pietsch in his book *History of Banach Spaces and Linear Operators*, the reason the later volumes never appeared was that "the development was too vigorous. Thus, in order to finish this project, a complete rewriting would have been necessary". Even still, the influence of volumes I and II in Banach space theory has been exceedingly nontrivial; indeed, Pietsch also writes: "The two-volume treatise of Lindenstrauss/Tzafriri on *Classical Banach Spaces* has become the most important reference of the modern period".