Microelectronic devices include a stack structure having a vertically alternating sequence of insulative structures and conductive structures arranged in tiers. At least one stadium, of stadiums within the stack structure, comprise staircase(s) having steps provided by a group of the conductive structures. Step contacts extend to the steps of the staircase(s) of the at least one of the stadiums. Each conductive structure of the group of conductive structures has more than one of the step contacts in contact therewith at at least one of the steps of the staircase(s). Additional microelectronic devices are also disclosed, as are methods of fabrication and electronic systems.