Mitochondria—Striking a balance between host and endosymbiont

Putting a price on the powerhouse Mitochondria—the so-called powerhouse of the cell—are derived from bacterial endosymbionts. This history provides opportunities and challenges for their host cells, particularly metazoans, including humans. Youle reviews the interplay between host and mitochondrial biology and highlights how mitochondrial ancestry has influenced innate immune responses. Keeping mitochondria both healthy and in check is key to organismal health and, when perturbed, leads to a variety of pathologies, including Parkinson's disease and inflammation. Science , this issue p. eaaw9855