A method of forming a microelectronic device comprises forming a microelectronic device structure assembly comprising memory cells, digit lines coupled to the memory cells, contact structures coupled to the digit lines, word lines coupled to the memory cells, additional contact structures coupled to the word lines, and isolation material surrounding the contact structures and the additional contact structures and overlying the memory cells. An additional microelectronic device structure assembly is formed and comprises control logic devices, further contact structures coupled to the control logic devices, and additional isolation material surrounding the further contact structures and overlying the control logic devices. The additional microelectronic device structure assembly is attached to the microelectronic device structure assembly by bonding the additional isolation material to the isolation material and by bonding the further contact structures to the contact structures and the additional contact structures. Microelectronic devices and electronic systems are also described.