The RenderMan® Interface Specification, the RISpec, is the official technical specification for the RenderMan Interface.
The RISpec 3.2
Version 3.2 of the RenderMan Interface Specification is the most recent version of the RI Spec. It supercedes version 3.1, originally published in September, 1989. Version 3.2 contains substantial improvements, updates, and enhancements over its precursor.
The RISpec 3.1
This document is version 3.1 of the RenderMan Interface Specification of September, 1989. It supercedes version 3.0, originally published in May, 1988. Version 3.1 introduces a second binding for the RenderMan Interface: the RenderMan Interface Bytestream Protocol (RIB).