Nowadays, NAND Flash technology is everywhere, since it is the core of the code and data storage in mobile and embedded applications; moreover, its market share is exploding with Solid-State-Drives (SSDs), which are replacing Hard Disk Drives (HDDs) in consumer and enterprise scenarios. To keep the evolutionary pace of the technology, NAND Flash must scale aggressively in terms of bit cost. When approaching ultra-scaled technologies, planar NAND is hitting a wall: both academia researchers and industry worked to cope with this issue for several decades. Then, the 3D integration approach turned out to be the definitive alternative by eventually reaching mass production. This review paper exposes several 3D NAND Flash memory technologies, along with their related integration challenges, by showing their different layouts, scaling trends and performance/reliability features.