ISO/IEC/TS 18661-2:2015 extends programming language C as specified in ISO/IEC 9899:2011, (C11) with changes specified in ISO/IEC/TS 18661-1, to support decimal floating-point arithmetic conforming to ISO/IEC/IEEE 60559:2011. It covers all requirements of IEC 60559 as they pertain to C decimal floating types.

ISO/IEC/TS 18661-2:2015 does not cover binary floating-point arithmetic (which is covered in ISO/IEC/TS 18661-1), nor does it cover most optional features of IEC 60559.