This volume serves as the definitive technical reference for the NeXTstep programming interface, addressing the core question of how developers can effectively utilize the system's object-oriented framework. Authored by the engineering team at NeXT Computer Inc., the text provides the foundational documentation required to build applications within the NeXT environment. It outlines the specific class hierarchies, messaging protocols, and interface components that define the NeXTstep development experience.

Experts and historical computing enthusiasts recognize this as a foundational text for understanding the evolution of modern object-oriented operating systems. Readers frequently note the high level of technical density, as the prose is written specifically for software engineers working within the NeXT hardware ecosystem.