A method of forming a microelectronic device comprises forming a microelectronic device structure comprising memory cells, digit lines, word lines, and at least one isolation material covering and surrounding the memory cells, the digit lines, and the word lines. An additional microelectronic device structure comprising control logic devices and at least one additional isolation material covering and surrounding the control logic devices is formed. The additional microelectronic device structure is attached to the microelectronic device structure. Contact structures are formed to extend through the at least one isolation material and the at least one additional isolation material. Some of the contact structures are coupled to some of the digit lines and some of the control logic devices. Some other of the contact structures are coupled to some of the word lines and some other of the control logic devices. Microelectronic devices, electronic systems, and additional methods are also described.