CIA stands for '''C'''TR '''I'''mportable '''A'''rchive. These files contain a compiled application which can be installed on CTR NAND, TWL NAND (part of the NAND used by DSi applications) and on the SD card. CIA files can be created with the Nintendo 3DS SDK and installed on the 3DS test units by the Dev Menu.
=== Format ===
The CIA format based on [http://wiibrew.org/wiki/Wad WAD format], so the structure is very similar to the WAD structure.