This volume serves as the definitive technical reference for the NeXTSTEP development environment, addressing the core question of how developers can effectively interface with the system's object-oriented frameworks. The text is authored by the engineering team at NeXT Computer Inc., providing the primary documentation for the Objective-C based APIs and system services. It establishes the foundational framework for building applications within the NeXTSTEP ecosystem, focusing on class hierarchies, messaging protocols, and interface design.

Experts and developers of the era identify this as the foundational text for mastering the NeXTSTEP platform. Readers frequently note the high density of technical information and the necessity of this manual for any serious development work on NeXT hardware.