Eiffel: The Language
Eiffel: The Language by Bertrand Meyer.
Prentice Hall Object-Oriented Series.
Eiffel: The Language is one of the foundation volumes of Eiffel technology. It was originally published in 1992, and reprinted later with updates and corrections.
Because the language specification has changed since the last reprinting to incorporate new quality and productivity constructs, hardcopies of Eiffel: The Language, although still available, will represent the bulk of Eiffel correctly, but will not reflect the latest important changes.
Currently Standard Eiffel, the successor to Eiffel: The Language, is a work-in-progress and is available in its current state online (See Standard Eiffel, on this page).
The most current state of Eiffel syntax, validity, and semantics is described in the ISO/ECMA standard document, also available online.