Mitochondria have been strongly implicated in neurodegenerative diseases such as Parkinson’s, Huntington’s and amyotrophic lateral sclerosis. They are also affected in cancer, ageing and cardiovascular disease. The final section of the book reviews mitochondrial mutations and their consequences in ageing and other phenotypic manifestations. The authors discuss how mitochondrial proteins might constitute important therapeutic targets and describe initial attempts to develop compounds that can regulate their function.