A microelectronic device comprises a stack structure comprising alternating conductive structures and insulative structures arranged in tiers, each of the tiers individually comprising a conductive structure and an insulative structure, strings of memory cells vertically extending through the stack structure, the strings of memory cells comprising a channel material vertically extending through the stack structure, and conductive rails laterally adjacent to the conductive structures of the stack structure. The conductive rails comprise a material composition that is different than a material composition of the conductive structures of the stack structure. Related memory devices, electronic systems, and methods are also described.