This chapter describes the general structure and organization of memory in microcontrollers, in particular medium-end PICs. The chapter begins by defining basic memory concepts, including word, address, and memory size. This is followed by the description of the two methods to organize memory in microcontrollers: linear memory and paged memory. The chapter then describes several technologies used for memory fabrication and finishes by explaining how memory is organized in medium-end PIC microcontrollers.