An address constant is an absolute or relocatable expression, such as a storage address, that is translated into a constant. Address constants can be used for initializing base registers to facilitate the addressing of storage. Furthermore, they provide a means of communicating between control sections of a multisection program. However, storage addressing and control section communication also depends on the USING assembler instruction and the loading of registers. See USING instruction.

The nominal value of an address constant, unlike other types of constants, is enclosed in parentheses. If two or more address constants are specified in an operand, they are separated by commas, and the whole sequence is enclosed by parentheses. There are seven types of address constants: A, Y, S, R, Q, J, and V. A relocatable address constant cannot be specified with bit lengths.