Today, flash memory are strongly used in the embedded system domain. NAND flash memories are the building block of main secondary storage systems. Such memories present many benefits in terms of data density, I/O performance, shock resistance and power consumption. Nevertheless, flash does not come without constraints: the write / erase granularity asymmetry and the limited lifetime bring the need for specific management. This can be done through the operating system using dedicated Flash File Systems (FFSs). In this document, we present general concepts about FFSs, and implementations example that are JFFS2, YAFFS2 and UBIFS, the most commonly used flash file systems. Then we give performance evaluation results for these FFSs.