An excellent introduction to OO software design from a formalist viewpoint, based around, but not dependent on, the Eiffel language.
Denotational and axiomatic semantics for the masses.
The book of the language, from its inventor, written in his usual discursive style. A good read for understanding the language, rather harder, but still possible, to use as a laguange reference.
A complete reworking of the first edition, and extended to cover new areas. Some think this long-awaited second edition is not an improvement on its slimmer original. I haven't read it yet.
Introduces The Seven Sins of the Specifier