Mitochondria are essential organelles found in every eukaryotic cell, required to convert food into usable energy. The mitochondrial oxidative phosphorylation (OXPHOS) system, which produces the majority of cellular energy in the form of ATP, is controlled by two distinct genomes: the nuclear and the mitochondrial genome (mtDNA). Mutations in mitochondrial genes encoded by either genome could cause diseases affecting OXPHOS system, called mitochondrial diseases, whose prevalence has been estimated to be ≈1:8500. Moreover, dysfunction of mitochondrial OXPHOS system has emerged as a key factor in a myriad of “common” diseases, including neurodegenerative and metabolic disorders like Parkinson’s and Alzheimer’s Disease, Type 2 Diabetes, and was linked to aging process. Despite all this, it is surprising that our understanding of the mechanisms governing the mitochondrial gene expression and its associated pathologies remain superficial and therapeutic interventions unexplored. The basic machineries for mtDNA replication, mtDNA transcription and mitochondrial translation are known, but the regulation of these processes in response to metabolic demands is poorly understood. The complex nature of mitochondrial gene expression that relies on two different genomes calls for a multidisciplinary approach where different teams of researchers join forces. Studies in this area are not only of basic scientific interest but may also provide new avenues towards treatment of mitochondrial dysfunction in a variety of human diseases.The key aim of the REMIX Network is combine the skills of European research groups to provide strategic training of the next generation of scientists through a programme that will progress in the elucidation of the molecular mechanisms and pathways that regulate mitochondrial gene expression.