Memory circuitry comprising strings of memory cells comprising memory blocks individually comprises a vertical stack comprising alternating insulative tiers and conductive tiers. Channel-material strings of memory cells extend through the insulative tiers and the conductive tiers in a memory-array region. The insulative tiers and the conductive tiers of the memory blocks extend from the memory-array region into a stair-step region. Individual of the memory blocks in the stair-step region comprise a flight of operative stairs. Individual of the operative stairs comprise one of the conductive tiers. At least some immediately-laterally-adjacent of the individual memory blocks in the stair-step region have their flights of operative stairs laterally-separated by a stack comprising two vertically-alternating different-composition insulative materials. Other embodiments, including method, are disclosed.