**1. Introduction**

The ERR family of transcription factors are orphan NRs that are characterized for their functions in the transcriptional regulation of genes involved in mitochondrial bioenergetics and function [1]. Members of the ERR family orphan NRs regulate a range of cellular functions, including OXPHOS as well as glucose and lipid metabolism [2] and play critical roles in the transcriptional regulation of genes involved in mitochondrial bioenergetics, TCA cycle, mitochondrial OXPHOS, and fatty acid β-oxidation [3]. The ERRs in general serve as positive transcriptional regulators of genes regulating mitochondrial respiration and negative regulators for genes

regulating gluconeogenesis [4–6]. These properties make ERRs potential targets for understanding and treating metabolic diseases, particularly T2D, IR, and obesity. In this review, we will summarize the overall function of ERRs and their regulations. We will then focus on their roles in the development of liver steatosis, particularly NAFLD and non-alcoholic steatohepatitis (NASH).
