Abstract Mitochondrial respiratory chain diseases are the most prevalent group of inherited neurometabolic disorders and are clinically, biochemically, and genetically heterogeneous. They may present at any stage of life and often manifest with severe multisystem disease, although single organ involvement is characteristic of some conditions such as Leber hereditary optic neuropathy. As a result of these complexities, the diagnostic pathway is often challenging, so too is further advice, guidance, and therapy following diagnosis. Difficulties also occur with regard to genetic counseling, prognostic assessment, and treatment; there is still no cure or even agreed standards of treatment available for these debilitating diseases. Limited therapeutic options and a lack of curative treatment have led to physicians prescribing individual “trials of therapy” for which no evidence-based recommendations are available. However, new therapeutic options are the focus of active molecular genetic, biochemical, and clinical research, and some medicinal compounds have achieved international governmental approval. In this chapter, we summarize these advances and provide a broad overview of the treatment and novel approaches to preventing transmission of mitochondrial disease.