Apple Human Interface Guidelines (aka HIG, 1987)

The first edition of Apple’s book on human interface design, meant both to explain the rationale behind the design of the Lisa and Macintosh interfaces, and also to guide developers in implementing applications. It’s remarkably detailed in its rationale, and it’s written with careful clarity.

The high-level principles capture much of what designers do intuitively today, but the explanations—which were novel at the time—help explain why these have become such standard behaviors.

The extended discussion of the controls and elements of the Macintosh interface are mostly of historical and background interest.

Also contains a surprisingly thorough bibliography.