Non-alcoholic steatohepatitis (NASH) can be considered the pandemic of these times, because of its global diffusion alongside obesity, diabetes, and metabolic dysfunction. It is a disease that often poses many difficulties, since making an early diagnosis is often impossible since specific diagnostic tests and criteria are missing: so, it needs a high degree of suspicion. Most of the times the evolution to its more severe and terminal step, NASH cirrhosis, is unavoidable and so are the social pressure on health system and economic consequences it brings back. The aim of this article is to provide a review of the literature about both non-alcoholic fatty liver disease (NAFLD) and NASH, thus structuring a wide, comprehensive, 360-degree work with a focus on all major aspects of NAFLD, spanning from diagnosis, physiopathology and its repercussions on liver transplantation. Moreover, we also focus on patients related issues both in pre- and post-transplant management (when these patients are listed for liver transplant). NAFLD and NASH are a contemporary plague, and an exhaustive knowledge of the problem throughout all its aspects is necessary in order to lower economic weight that metabolic issues bring back and to have an open view to possible solutions to all management issues that NASH patients have and that are often prohibitive to a definitive cure (for example cardiovascular risk in patients otherwise eligible to liver transplantation). We aim to offer a complete view on the actual knowledge about NAFLD and NASH, by an extensive review of the literature.