Magnetic tunnel junction magnetoresistive random-access memory (MTJ-MRAM) appears to be in an advanced stage of development at several companies, including Motorola Inc., IBM Corporation, Infineon Technologies and Cypress Semiconductor Corp. MRAM has the potential to become a universal memory technology, with the high speed of SRAM, the nonvolatility of flash memory (but with much greater write-erase endurance than flash memory), and with storage densities that could approach those of DRAM. MRAM is embeddable in conventional CMOS processes with as few as four additional masks. We briefly review early MRAM technologies such as anisotropic MRAM, spin valve MRAM, and pseudo spin valve MRAM. Then we survey both conventional MTJ-MRAM and the recently-developed read-before-write toggle-mode MTJ-MRAM.