The CIF API is a reference application programming interface and implementation for the Crystallographic Information Framework. It was commissioned by COMCIFS to manipulate CIF data conforming to both syntax versions 1.1 and 2.0 and to handle all the content features that might be found in both CIF data and dictionary files. It is written in a portable C form. It consists of two parts: (a) data types, function specifications, constants, and macro definitions jointly constituting an interface between programs that consume, manipulate, and produce CIF data and an underlying support library, and (b) an implementation of the interface functions and data types. It provides for both object-model in-memory and event-driven parsing strategies, and is accompanied by a test suite and example programs.